analysis and synthesis in literature review

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How to Write a Literature Review

  • 6. Synthesize
  • Literature Reviews: A Recap
  • Reading Journal Articles
  • Does it Describe a Literature Review?
  • 1. Identify the Question
  • 2. Review Discipline Styles
  • Searching Article Databases
  • Finding Full-Text of an Article
  • Citation Chaining
  • When to Stop Searching
  • 4. Manage Your References
  • 5. Critically Analyze and Evaluate

Synthesis Visualization

Synthesis matrix example.

  • 7. Write a Literature Review

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  • Synthesis Worksheet

About Synthesis

What is synthesis? What synthesis is NOT:

Approaches to Synthesis

You can sort the literature in various ways, for example:

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How to Begin?

Read your sources carefully and find the main idea(s) of each source

Look for similarities in your sources – which sources are talking about the same main ideas? (for example, sources that discuss the historical background on your topic)

Use the worksheet (above) or synthesis matrix (below) to get organized

This work can be messy. Don't worry if you have to go through a few iterations of the worksheet or matrix as you work on your lit review!

Four Examples of Student Writing

In the four examples below, only ONE shows a good example of synthesis: the fourth column, or  Student D . For a web accessible version, click the link below the image.

Four Examples of Student Writing; Follow the "long description" infographic link for a web accessible description.

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Click on the example to view the pdf.

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analysis and synthesis in literature review

Literature Syntheis 101

How To Synthesise The Existing Research (With Examples)

By: Derek Jansen (MBA) | Expert Reviewer: Eunice Rautenbach (DTech) | August 2023

One of the most common mistakes that students make when writing a literature review is that they err on the side of describing the existing literature rather than providing a critical synthesis of it. In this post, we’ll unpack what exactly synthesis means and show you how to craft a strong literature synthesis using practical examples.

This post is based on our popular online course, Literature Review Bootcamp . In the course, we walk you through the full process of developing a literature review, step by step. If it’s your first time writing a literature review, you definitely want to use this link to get 50% off the course (limited-time offer).

Overview: Literature Synthesis

  • What exactly does “synthesis” mean?
  • Aspect 1: Agreement
  • Aspect 2: Disagreement
  • Aspect 3: Key theories
  • Aspect 4: Contexts
  • Aspect 5: Methodologies
  • Bringing it all together

What does “synthesis” actually mean?

As a starting point, let’s quickly define what exactly we mean when we use the term “synthesis” within the context of a literature review.

Simply put, literature synthesis means going beyond just describing what everyone has said and found. Instead, synthesis is about bringing together all the information from various sources to present a cohesive assessment of the current state of knowledge in relation to your study’s research aims and questions .

Put another way, a good synthesis tells the reader exactly where the current research is “at” in terms of the topic you’re interested in – specifically, what’s known , what’s not , and where there’s a need for more research .

So, how do you go about doing this?

Well, there’s no “one right way” when it comes to literature synthesis, but we’ve found that it’s particularly useful to ask yourself five key questions when you’re working on your literature review. Having done so,  you can then address them more articulately within your actual write up. So, let’s take a look at each of these questions.

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1. Points Of Agreement

The first question that you need to ask yourself is: “Overall, what things seem to be agreed upon by the vast majority of the literature?”

For example, if your research aim is to identify which factors contribute toward job satisfaction, you’ll need to identify which factors are broadly agreed upon and “settled” within the literature. Naturally, there may at times be some lone contrarian that has a radical viewpoint , but, provided that the vast majority of researchers are in agreement, you can put these random outliers to the side. That is, of course, unless your research aims to explore a contrarian viewpoint and there’s a clear justification for doing so. 

Identifying what’s broadly agreed upon is an essential starting point for synthesising the literature, because you generally don’t want (or need) to reinvent the wheel or run down a road investigating something that is already well established . So, addressing this question first lays a foundation of “settled” knowledge.

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analysis and synthesis in literature review

2. Points Of Disagreement

Related to the previous point, but on the other end of the spectrum, is the equally important question: “Where do the disagreements lie?” .

In other words, which things are not well agreed upon by current researchers? It’s important to clarify here that by disagreement, we don’t mean that researchers are (necessarily) fighting over it – just that there are relatively mixed findings within the empirical research , with no firm consensus amongst researchers.

This is a really important question to address as these “disagreements” will often set the stage for the research gap(s). In other words, they provide clues regarding potential opportunities for further research, which your study can then (hopefully) contribute toward filling. If you’re not familiar with the concept of a research gap, be sure to check out our explainer video covering exactly that .

analysis and synthesis in literature review

3. Key Theories

The next question you need to ask yourself is: “Which key theories seem to be coming up repeatedly?” .

Within most research spaces, you’ll find that you keep running into a handful of key theories that are referred to over and over again. Apart from identifying these theories, you’ll also need to think about how they’re connected to each other. Specifically, you need to ask yourself:

  • Are they all covering the same ground or do they have different focal points  or underlying assumptions ?
  • Do some of them feed into each other and if so, is there an opportunity to integrate them into a more cohesive theory?
  • Do some of them pull in different directions ? If so, why might this be?
  • Do all of the theories define the key concepts and variables in the same way, or is there some disconnect? If so, what’s the impact of this ?

Simply put, you’ll need to pay careful attention to the key theories in your research area, as they will need to feature within your theoretical framework , which will form a critical component within your final literature review. This will set the foundation for your entire study, so it’s essential that you be critical in this area of your literature synthesis.

If this sounds a bit fluffy, don’t worry. We deep dive into the theoretical framework (as well as the conceptual framework) and look at practical examples in Literature Review Bootcamp . If you’d like to learn more, take advantage of our limited-time offer to get 60% off the standard price.

analysis and synthesis in literature review

4. Contexts

The next question that you need to address in your literature synthesis is an important one, and that is: “Which contexts have (and have not) been covered by the existing research?” .

For example, sticking with our earlier hypothetical topic (factors that impact job satisfaction), you may find that most of the research has focused on white-collar , management-level staff within a primarily Western context, but little has been done on blue-collar workers in an Eastern context. Given the significant socio-cultural differences between these two groups, this is an important observation, as it could present a contextual research gap .

In practical terms, this means that you’ll need to carefully assess the context of each piece of literature that you’re engaging with, especially the empirical research (i.e., studies that have collected and analysed real-world data). Ideally, you should keep notes regarding the context of each study in some sort of catalogue or sheet, so that you can easily make sense of this before you start the writing phase. If you’d like, our free literature catalogue worksheet is a great tool for this task.

5. Methodological Approaches

Last but certainly not least, you need to ask yourself the question: “What types of research methodologies have (and haven’t) been used?”

For example, you might find that most studies have approached the topic using qualitative methods such as interviews and thematic analysis. Alternatively, you might find that most studies have used quantitative methods such as online surveys and statistical analysis.

But why does this matter?

Well, it can run in one of two potential directions . If you find that the vast majority of studies use a specific methodological approach, this could provide you with a firm foundation on which to base your own study’s methodology . In other words, you can use the methodologies of similar studies to inform (and justify) your own study’s research design .

On the other hand, you might argue that the lack of diverse methodological approaches presents a research gap , and therefore your study could contribute toward filling that gap by taking a different approach. For example, taking a qualitative approach to a research area that is typically approached quantitatively. Of course, if you’re going to go against the methodological grain, you’ll need to provide a strong justification for why your proposed approach makes sense. Nevertheless, it is something worth at least considering.

Regardless of which route you opt for, you need to pay careful attention to the methodologies used in the relevant studies and provide at least some discussion about this in your write-up. Again, it’s useful to keep track of this on some sort of spreadsheet or catalogue as you digest each article, so consider grabbing a copy of our free literature catalogue if you don’t have anything in place.

Looking at the methodologies of existing, similar studies will help you develop a strong research methodology for your own study.

Bringing It All Together

Alright, so we’ve looked at five important questions that you need to ask (and answer) to help you develop a strong synthesis within your literature review.  To recap, these are:

  • Which things are broadly agreed upon within the current research?
  • Which things are the subject of disagreement (or at least, present mixed findings)?
  • Which theories seem to be central to your research topic and how do they relate or compare to each other?
  • Which contexts have (and haven’t) been covered?
  • Which methodological approaches are most common?

Importantly, you’re not just asking yourself these questions for the sake of asking them – they’re not just a reflection exercise. You need to weave your answers to them into your actual literature review when you write it up. How exactly you do this will vary from project to project depending on the structure you opt for, but you’ll still need to address them within your literature review, whichever route you go.

The best approach is to spend some time actually writing out your answers to these questions, as opposed to just thinking about them in your head. Putting your thoughts onto paper really helps you flesh out your thinking . As you do this, don’t just write down the answers – instead, think about what they mean in terms of the research gap you’ll present , as well as the methodological approach you’ll take . Your literature synthesis needs to lay the groundwork for these two things, so it’s essential that you link all of it together in your mind, and of course, on paper.

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analysis and synthesis in literature review

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Get Organized

  • Lit Review Prep Use this template to help you evaluate your sources, create article summaries for an annotated bibliography, and a synthesis matrix for your lit review outline.

Synthesize your Information

Synthesize: combine separate elements to form a whole.

Synthesis Matrix

A synthesis matrix helps you record the main points of each source and document how sources relate to each other.

After summarizing and evaluating your sources, arrange them in a matrix or use a citation manager to help you see how they relate to each other and apply to each of your themes or variables.  

By arranging your sources by theme or variable, you can see how your sources relate to each other, and can start thinking about how you weave them together to create a narrative.

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Literature Review Basics

  • What is a Literature Review?
  • Synthesizing Research
  • Using Research & Synthesis Tables
  • Additional Resources

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Synthesis: What is it?

First, let's be perfectly clear about what synthesizing your research isn't :

  • - It isn't  just summarizing the material you read
  • - It isn't  generating a collection of annotations or comments (like an annotated bibliography)
  • - It isn't  compiling a report on every single thing ever written in relation to your topic

When you  synthesize  your research, your job is to help your reader understand the current state of the conversation on your topic, relative to your research question.  That may include doing the following:

  • - Selecting and using representative work on the topic
  • - Identifying and discussing trends in published data or results
  • - Identifying and explaining the impact of common features (study populations, interventions, etc.) that appear frequently in the literature
  • - Explaining controversies, disputes, or central issues in the literature that are relevant to your research question
  • - Identifying gaps in the literature, where more research is needed
  • - Establishing the discussion to which your own research contributes and demonstrating the value of your contribution

Essentially, you're telling your reader where they are (and where you are) in the scholarly conversation about your project.

Synthesis: How do I do it?

Synthesis, step by step.

This is what you need to do  before  you write your review.

  • Identify and clearly describe your research question (you may find the Formulating PICOT Questions table at  the Additional Resources tab helpful).
  • Collect sources relevant to your research question.
  • Organize and describe the sources you've found -- your job is to identify what  types  of sources you've collected (reviews, clinical trials, etc.), identify their  purpose  (what are they measuring, testing, or trying to discover?), determine the  level of evidence  they represent (see the Levels of Evidence table at the Additional Resources tab ), and briefly explain their  major findings . Use a Research Table to document this step.
  • Study the information you've put in your Research Table and examine your collected sources, looking for  similarities  and  differences . Pay particular attention to  populations ,   methods  (especially relative to levels of evidence), and  findings .
  • Analyze what you learn in (4) using a tool like a Synthesis Table. Your goal is to identify relevant themes, trends, gaps, and issues in the research.  Your literature review will collect the results of this analysis and explain them in relation to your research question.

Analysis tips

  • - Sometimes, what you  don't  find in the literature is as important as what you do find -- look for questions that the existing research hasn't answered yet.
  • - If any of the sources you've collected refer to or respond to each other, keep an eye on how they're related -- it may provide a clue as to whether or not study results have been successfully replicated.
  • - Sorting your collected sources by level of evidence can provide valuable insight into how a particular topic has been covered, and it may help you to identify gaps worth addressing in your own work.
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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

  • An introductory paragraph that explains what your working topic and thesis is
  • A forecast of key topics or texts that will appear in the review
  • Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
  • Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
  • Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
  • Critically Evaluate: Mention the strengths and weaknesses of your sources
  • Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

  • Summarize the key findings you have taken from the literature and emphasize their significance
  • Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

  • Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
  • Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
  • Qualitative versus quantitative research
  • Empirical versus theoretical scholarship
  • Divide the research by sociological, historical, or cultural sources
  • Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

  • It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
  • Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
  • Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
  • Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

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  • Synthesizing Sources | Examples & Synthesis Matrix

Synthesizing Sources | Examples & Synthesis Matrix

Published on July 4, 2022 by Eoghan Ryan . Revised on May 31, 2023.

Synthesizing sources involves combining the work of other scholars to provide new insights. It’s a way of integrating sources that helps situate your work in relation to existing research.

Synthesizing sources involves more than just summarizing . You must emphasize how each source contributes to current debates, highlighting points of (dis)agreement and putting the sources in conversation with each other.

You might synthesize sources in your literature review to give an overview of the field or throughout your research paper when you want to position your work in relation to existing research.

Table of contents

Example of synthesizing sources, how to synthesize sources, synthesis matrix, other interesting articles, frequently asked questions about synthesizing sources.

Let’s take a look at an example where sources are not properly synthesized, and then see what can be done to improve it.

This paragraph provides no context for the information and does not explain the relationships between the sources described. It also doesn’t analyze the sources or consider gaps in existing research.

Research on the barriers to second language acquisition has primarily focused on age-related difficulties. Building on Lenneberg’s (1967) theory of a critical period of language acquisition, Johnson and Newport (1988) tested Lenneberg’s idea in the context of second language acquisition. Their research seemed to confirm that young learners acquire a second language more easily than older learners. Recent research has considered other potential barriers to language acquisition. Schepens, van Hout, and van der Slik (2022) have revealed that the difficulties of learning a second language at an older age are compounded by dissimilarity between a learner’s first language and the language they aim to acquire. Further research needs to be carried out to determine whether the difficulty faced by adult monoglot speakers is also faced by adults who acquired a second language during the “critical period.”

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To synthesize sources, group them around a specific theme or point of contention.

As you read sources, ask:

  • What questions or ideas recur? Do the sources focus on the same points, or do they look at the issue from different angles?
  • How does each source relate to others? Does it confirm or challenge the findings of past research?
  • Where do the sources agree or disagree?

Once you have a clear idea of how each source positions itself, put them in conversation with each other. Analyze and interpret their points of agreement and disagreement. This displays the relationships among sources and creates a sense of coherence.

Consider both implicit and explicit (dis)agreements. Whether one source specifically refutes another or just happens to come to different conclusions without specifically engaging with it, you can mention it in your synthesis either way.

Synthesize your sources using:

  • Topic sentences to introduce the relationship between the sources
  • Signal phrases to attribute ideas to their authors
  • Transition words and phrases to link together different ideas

To more easily determine the similarities and dissimilarities among your sources, you can create a visual representation of their main ideas with a synthesis matrix . This is a tool that you can use when researching and writing your paper, not a part of the final text.

In a synthesis matrix, each column represents one source, and each row represents a common theme or idea among the sources. In the relevant rows, fill in a short summary of how the source treats each theme or topic.

This helps you to clearly see the commonalities or points of divergence among your sources. You can then synthesize these sources in your work by explaining their relationship.

Example: Synthesis matrix
Lenneberg (1967) Johnson and Newport (1988) Schepens, van Hout, and van der Slik (2022)
Approach Primarily theoretical, due to the ethical implications of delaying the age at which humans are exposed to language Testing the English grammar proficiency of 46 native Korean or Chinese speakers who moved to the US between the ages of 3 and 39 (all participants had lived in the US for at least 3 years at the time of testing) Analyzing the results of 56,024 adult immigrants to the Netherlands from 50 different language backgrounds
Enabling factors in language acquisition A critical period between early infancy and puberty after which language acquisition capabilities decline A critical period (following Lenneberg) General age effects (outside of a contested critical period), as well as the similarity between a learner’s first language and target language
Barriers to language acquisition Aging Aging (following Lenneberg) Aging as well as the dissimilarity between a learner’s first language and target language

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analysis and synthesis in literature review

Synthesizing sources means comparing and contrasting the work of other scholars to provide new insights.

It involves analyzing and interpreting the points of agreement and disagreement among sources.

You might synthesize sources in your literature review to give an overview of the field of research or throughout your paper when you want to contribute something new to existing research.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

Topic sentences help keep your writing focused and guide the reader through your argument.

In an essay or paper , each paragraph should focus on a single idea. By stating the main idea in the topic sentence, you clarify what the paragraph is about for both yourself and your reader.

At college level, you must properly cite your sources in all essays , research papers , and other academic texts (except exams and in-class exercises).

Add a citation whenever you quote , paraphrase , or summarize information or ideas from a source. You should also give full source details in a bibliography or reference list at the end of your text.

The exact format of your citations depends on which citation style you are instructed to use. The most common styles are APA , MLA , and Chicago .

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Ryan, E. (2023, May 31). Synthesizing Sources | Examples & Synthesis Matrix. Scribbr. Retrieved September 9, 2024, from https://www.scribbr.com/working-with-sources/synthesizing-sources/

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Literature Reviews

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  • Getting started
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  • 1. Define your research question
  • 2. Plan your search
  • 3. Search the literature
  • 4. Organize your results

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In the synthesis step of a literature review, researchers analyze and integrate information from selected sources to identify patterns and themes. This involves critically evaluating findings, recognizing commonalities, and constructing a cohesive narrative that contributes to the understanding of the research topic.

Synthesis Not synthesis
✔️ Analyzing and integrating information ❌ Simply summarizing individual studies or articles
✔️ Identifying patterns and themes ❌ Listing facts without interpretation
✔️ Critically evaluating findings ❌ Copy-pasting content from sources
✔️ Constructing a cohesive narrative ❌ Providing personal opinions
✔️ Recognizing commonalities ❌ Focusing only on isolated details
✔️ Generating new perspectives ❌ Repeating information verbatim

Here are some examples of how to approach synthesizing the literature:

💡 By themes or concepts

🕘 Historically or chronologically

📊 By methodology

These organizational approaches can also be used when writing your review. It can be beneficial to begin organizing your references by these approaches in your citation manager by using folders, groups, or collections.

Create a synthesis matrix

A synthesis matrix allows you to visually organize your literature.

Topic: ______________________________________________

  Source #2 Source #3 Source #4
       
       

Topic: Chemical exposure to workers in nail salons

  Gutierrez et al. 2015 Hansen 2018 Lee et al. 2014
"Participants reported multiple episodes of asthma over one year" (p. 58)    
"Nail salon workers who did not wear gloves routinely reported increased episodes of contact dermatitis" (p. 115)      
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Literature Review How To

  • Things To Consider
  • Synthesizing Sources
  • Video Tutorials
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What is Synthesis

What is Synthesis? Synthesis writing is a form of analysis related to comparison and contrast, classification and division. On a basic level, synthesis requires the writer to pull together two or more summaries, looking for themes in each text. In synthesis, you search for the links between various materials in order to make your point. Most advanced academic writing, including literature reviews, relies heavily on synthesis. (Temple University Writing Center)  

How To Synthesize Sources in a Literature Review

Literature reviews synthesize large amounts of information and present it in a coherent, organized fashion. In a literature review you will be combining material from several texts to create a new text – your literature review.

You will use common points among the sources you have gathered to help you synthesize the material. This will help ensure that your literature review is organized by subtopic, not by source. This means various authors' names can appear and reappear throughout the literature review, and each paragraph will mention several different authors. 

When you shift from writing summaries of the content of a source to synthesizing content from sources, there is a number things you must keep in mind: 

  • Look for specific connections and or links between your sources and how those relate to your thesis or question.
  • When writing and organizing your literature review be aware that your readers need to understand how and why the information from the different sources overlap.
  • Organize your literature review by the themes you find within your sources or themes you have identified. 
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Literature Reviews

  • Introduction
  • Tutorials and resources
  • Step 1: Literature search
  • Step 2: Analysis, synthesis, critique
  • Step 3: Writing the review

If you need any assistance, please contact the library staff at the Georgia Tech Library Help website . 

Analysis, synthesis, critique

Literature reviews build a story. You are telling the story about what you are researching. Therefore, a literature review is a handy way to show that you know what you are talking about. To do this, here are a few important skills you will need.

Skill #1: Analysis

Analysis means that you have carefully read a wide range of the literature on your topic and have understood the main themes, and identified how the literature relates to your own topic. Carefully read and analyze the articles you find in your search, and take notes. Notice the main point of the article, the methodologies used, what conclusions are reached, and what the main themes are. Most bibliographic management tools have capability to keep notes on each article you find, tag them with keywords, and organize into groups.

Skill #2: Synthesis

After you’ve read the literature, you will start to see some themes and categories emerge, some research trends to emerge, to see where scholars agree or disagree, and how works in your chosen field or discipline are related. One way to keep track of this is by using a Synthesis Matrix .

Skill #3: Critique

As you are writing your literature review, you will want to apply a critical eye to the literature you have evaluated and synthesized. Consider the strong arguments you will make contrasted with the potential gaps in previous research. The words that you choose to report your critiques of the literature will be non-neutral. For instance, using a word like “attempted” suggests that a researcher tried something but was not successful. For example: 

There were some attempts by Smith (2012) and Jones (2013) to integrate a new methodology in this process.

On the other hand, using a word like “proved” or a phrase like “produced results” evokes a more positive argument. For example:

The new methodologies employed by Blake (2014) produced results that provided further evidence of X.

In your critique, you can point out where you believe there is room for more coverage in a topic, or further exploration in in a sub-topic.

Need more help?

If you are looking for more detailed guidance about writing your dissertation, please contact the folks in the Georgia Tech Communication Center .

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Literature reviews: synthesis.

  • Criticality

Synthesise Information

So, how can you create paragraphs within your literature review that demonstrates your knowledge of the scholarship that has been done in your field of study?  

You will need to present a synthesis of the texts you read.  

Doug Specht, Senior Lecturer at the Westminster School of Media and Communication, explains synthesis for us in the following video:  

Synthesising Texts  

What is synthesis? 

Synthesis is an important element of academic writing, demonstrating comprehension, analysis, evaluation and original creation.  

With synthesis you extract content from different sources to create an original text. While paraphrase and summary maintain the structure of the given source(s), with synthesis you create a new structure.  

The sources will provide different perspectives and evidence on a topic. They will be put together when agreeing, contrasted when disagreeing. The sources must be referenced.  

Perfect your synthesis by showing the flow of your reasoning, expressing critical evaluation of the sources and drawing conclusions.  

When you synthesise think of "using strategic thinking to resolve a problem requiring the integration of diverse pieces of information around a structuring theme" (Mateos and Sole 2009, p448). 

Synthesis is a complex activity, which requires a high degree of comprehension and active engagement with the subject. As you progress in higher education, so increase the expectations on your abilities to synthesise. 

How to synthesise in a literature review: 

Identify themes/issues you'd like to discuss in the literature review. Think of an outline.  

Read the literature and identify these themes/issues.  

Critically analyse the texts asking: how does the text I'm reading relate to the other texts I've read on the same topic? Is it in agreement? Does it differ in its perspective? Is it stronger or weaker? How does it differ (could be scope, methods, year of publication etc.). Draw your conclusions on the state of the literature on the topic.  

Start writing your literature review, structuring it according to the outline you planned.  

Put together sources stating the same point; contrast sources presenting counter-arguments or different points.  

Present your critical analysis.  

Always provide the references. 

The best synthesis requires a "recursive process" whereby you read the source texts, identify relevant parts, take notes, produce drafts, re-read the source texts, revise your text, re-write... (Mateos and Sole, 2009). 

What is good synthesis?  

The quality of your synthesis can be assessed considering the following (Mateos and Sole, 2009, p439):  

Integration and connection of the information from the source texts around a structuring theme. 

Selection of ideas necessary for producing the synthesis. 

Appropriateness of the interpretation.  

Elaboration of the content.  

Example of Synthesis

Original texts (fictitious): 

Animal testing is necessary to save human lives. Incidents have happened where humans have died or have been seriously harmed for using drugs that had not been tested on animals (Smith 2008).   

Animals feel pain in a way that is physiologically and neuroanatomically similar to humans (Chowdhury 2012).   

Animal testing is not always used to assess the toxicology of a drug; sometimes painful experiments are undertaken to improve the effectiveness of cosmetics (Turner 2015) 

Animals in distress can suffer psychologically, showing symptoms of depression and anxiety (Panatta and Hudson 2016). 

  

Synthesis: 

Animal experimentation is a subject of heated debate. Some argue that painful experiments should be banned. Indeed it has been demonstrated that such experiments make animals suffer physically and psychologically (Chowdhury 2012; Panatta and Hudson 2016). On the other hand, it has been argued that animal experimentation can save human lives and reduce harm on humans (Smith 2008). This argument is only valid for toxicological testing, not for tests that, for example, merely improve the efficacy of a cosmetic (Turner 2015). It can be suggested that animal experimentation should be regulated to only allow toxicological risk assessment, and the suffering to the animals should be minimised.   

Bibliography

Mateos, M. and Sole, I. (2009). Synthesising Information from various texts: A Study of Procedures and Products at Different Educational Levels. European Journal of Psychology of Education,  24 (4), 435-451. Available from https://doi.org/10.1007/BF03178760 [Accessed 29 June 2021].

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analysis and synthesis in literature review

What is a Literature Review? How to Write It (with Examples)

literature review

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

What is the purpose of literature review , a. habitat loss and species extinction: , b. range shifts and phenological changes: , c. ocean acidification and coral reefs: , d. adaptive strategies and conservation efforts: .

  • Choose a Topic and Define the Research Question: 
  • Decide on the Scope of Your Review: 
  • Select Databases for Searches: 
  • Conduct Searches and Keep Track: 
  • Review the Literature: 
  • Organize and Write Your Literature Review: 
  • How to write a literature review faster with Paperpal? 

Frequently asked questions 

What is a literature review .

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

analysis and synthesis in literature review

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

1. Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 

2. Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field.

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3. Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 

4. Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 

5. Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 

6. Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example 

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:  

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

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How to write a good literature review 

Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

  • Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
  • Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
  • Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
  • Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
  • Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

  • Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
  • Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
  • Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
  • Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
  • Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 
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Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

  • Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
  • Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
  • Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
  • Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
  • Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

what is a literature review

Conducting a literature review 

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:  

  • Select a topic that is relevant to your field of study. 
  • Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:  

  • Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
  • Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
  • Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:  

  • Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
  • Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:  

  • Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
  • Record and document your search strategy for transparency and replicability. 
  • Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:  

  • Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
  • Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
  • Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
  • Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
  • Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:  

  • Literature review outline should be based on themes, chronological order, or methodological approaches. 
  • Write a clear and coherent narrative that synthesizes the information gathered. 
  • Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
  • Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

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Paperpal Research Feature

  • Review and Save: Paperpal summarizes the information, while citing sources and listing relevant reads. You can quickly scan the results to identify relevant references and save these directly to your built-in citations library for later access. 
  • Cite with Confidence: Paperpal makes it easy to incorporate relevant citations and references in 10,000+ styles into your writing, ensuring your arguments are well-supported by credible sources. This translates to a polished, well-researched literature review. 

analysis and synthesis in literature review

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a good literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. By combining effortless research with an easy citation process, Paperpal Research streamlines the literature review process and empowers you to write faster and with more confidence. Try Paperpal Research now and see for yourself.  

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

  Annotated Bibliography  Literature Review 
Purpose  List of citations of books, articles, and other sources with a brief description (annotation) of each source.  Comprehensive and critical analysis of existing literature on a specific topic. 
Focus  Summary and evaluation of each source, including its relevance, methodology, and key findings.  Provides an overview of the current state of knowledge on a particular subject and identifies gaps, trends, and patterns in existing literature. 
Structure  Each citation is followed by a concise paragraph (annotation) that describes the source’s content, methodology, and its contribution to the topic.  The literature review is organized thematically or chronologically and involves a synthesis of the findings from different sources to build a narrative or argument. 
Length  Typically 100-200 words  Length of literature review ranges from a few pages to several chapters 
Independence  Each source is treated separately, with less emphasis on synthesizing the information across sources.  The writer synthesizes information from multiple sources to present a cohesive overview of the topic. 

References 

  • Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
  • Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
  • Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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Literature Synthesis: Guide To Synthesise & Write Literature Review

Literature synthesis is a crucial skill for researchers and scholars, allowing them to integrate findings from multiple sources into a coherent analysis. Mastering literature synthesis will enhance your research and writing skills. 

This guide will walk you through the process of synthesising and writing a literature review, providing practical steps and insider tips. Learn how to:

  • organise your sources,
  • identify key themes, and
  • create a cohesive narrative that highlights both agreements and disagreements within the existing literature.

Literature Synthesis vs Literature Review

You may be familiar with literature review, and the term literature synthesis may throw you off a bit. Are they a similar thing, or something different from each other?

If you are still unsure about how literature synthesis is different from literature review, here are a couple of points to think about: 

synthesize literature

Approach To Sources

One difference is the approach to sources. In a literature review, you might describe each source separately, detailing its findings and contributions.

With synthesis, you combine the ideas from multiple sources to highlight relationships and gaps.

One example would be you may find that several studies agree on a particular theme but use different methodologies to reach their conclusions.

Organisation

A second difference is the organization. Literature reviews typically follow a structured format, summarizing each source in a new paragraph.

In contrast, synthesis requires organising sources around key themes or topics. This might involve using a synthesis matrix to align findings and theories from different sources into a cohesive analysis.

How To Evaluate Literature

Evaluating the literature also differs. When you write a literature review, you summarise and describe the existing research. Synthesis goes further by:

  • critically evaluating the sources,
  • identifying points of agreement and disagreement, and
  • assessing the overall state of knowledge.

You need to address the methodological approaches used and how they relate to your research questions.

In terms of purpose, a literature review provides an overview of what’s known about a topic. It sets the stage for your research by summarising existing knowledge.

Synthesis, meanwhile, aims to create new insights by combining and contrasting different sources. This process helps you identify research gaps and questions that need further investigation.

Writing Process

Finally, the writing process differs. A literature review involves compiling summaries, often following a step-by-step guide.

With synthesis, you need to integrate:

  • theories, and
  • methodologies from various sources.

This involves weaving together different perspectives into a single, cohesive narrative that supports your research aims.

How To Perform Literature Synthesis?

Performing literature synthesis can be daunting, but by breaking it down step by step, you can create a comprehensive and coherent analysis of your topic.

Here’s a guide to help you through the process, with insider details and practical examples that will make your task easier.

Organise Your Sources

First, you need to gather and organise your sources. Start by conducting a thorough search of the existing literature on your topic, using

  • research guides,
  • library databases, and
  • academic journals to find relevant sources.

There are plenty of AI tools that can help with process as well – make sure you check out my guide on best AI tools for literature review.

Record the main points of each source in a summary table. This table should include columns for:

  • the author,
  • publication year,
  • key points,
  • methodologies used, and

By organising your sources in this way, you’ll have a clear overview of the existing literature.

Identify Themes

Once you have your sources organised, it’s time to start synthesising the literature. This means combining the ideas and findings from multiple sources to create a cohesive analysis.

Begin by identifying the key themes that emerge from your sources. These themes will form the basis of your synthesis.

synthesize literature

Suppose you are you’re researching job satisfaction, In this case, you might find recurring themes such as work-life balance, salary, and workplace environment.

Create A Synthesis Matrix

Next, create a synthesis matrix. This tool helps you organize the key points from each source under the identified themes.

Each row in the matrix represents a source, and each column represents a theme.

By filling in the matrix, you can see how different sources relate to each theme. This will help you identify similarities and differences between the sources.

Write Your Literature Synthesis

With your synthesis matrix in hand, you can start writing your literature synthesis.

Begin each paragraph with a clear topic sentence that identifies the theme you’re discussing. Then, weave together the findings from different sources, highlighting points of agreement and disagreement.

One way you may write this include: “While Franz (2008) found that salary is a major factor in job satisfaction, Goldstein (2012) argued that work-life balance plays a more significant role.”

Critically Evaluate Your Sources

Be sure to critically evaluate the sources as you synthesize the literature. This means assessing the methodologies used in each study and considering their impact on the findings.

Let’s say you found that most studies on job satisfaction used qualitative methods , you might question whether the findings would differ if quantitative methods were used. Addressing these methodological differences can help you identify research gaps and areas for further study.

analysis and synthesis in literature review

Don’t Just Summarise

As you write your paragraphs, avoid simply summarising each source. Instead, combine the key points from multiple sources to create a more comprehensive analysis.

If we reuse Franz (2008) as example, rather than describing Franz’s study in one paragraph and Goldstein’s study in another, integrate their findings to show how they relate to each other.

This approach will make your synthesis more cohesive and easier to follow.

Address The Broader Context Of The Topic

To create a strong synthesis, you also need to address the broader context of your research. This means considering the theoretical frameworks and empirical evidence that underpin your topic.

If you’re researching job satisfaction, you might discuss how different theories of motivation relate to your findings. By integrating these broader perspectives, you can provide a more comprehensive overview of the current state of knowledge.

Keep Questioning Yourself

Throughout the writing process, keep the five key questions in mind:

  • What’s broadly agreed upon within the current research?
  • Where do the disagreements lie?
  • Which theories are central to your research topic?
  • Which contexts have been covered, and which haven’t?
  • What types of research methodologies have been used?

Addressing these questions will help you create a more thorough and insightful synthesis.

Revise & Edit

Finally, revise and edit your work. This means checking for clarity, coherence, and logical flow. Make sure each paragraph has a clear topic sentence and that all sentences within the paragraph relate to that topic.

Remove any unnecessary information and ensure that your synthesis is well-organised and easy to follow.

analysis and synthesis in literature review

Your Guide To Synthesise Literature

Performing literature synthesis may seem overwhelming, but by following this step-by-step guide, you can create a comprehensive and cohesive analysis of your topic.

Use tools like summary tables and synthesis matrices to organise your sources, and focus on combining the key points from multiple sources to create a strong synthesis.

With careful planning and critical evaluation, you can produce a literature synthesis that provides valuable insights into your field of study.

analysis and synthesis in literature review

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A synthesis matrix visually represents your research by organizing your sources by themes:

  Theme #1 Theme #2 Theme #3
Source #1      
Source #2      
Source #3      
  • Sample Synthesis Matrix Example provided by Ashford University Writing Center .
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How to Synthesize Written Information from Multiple Sources

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When you write a literature review or essay, you have to go beyond just summarizing the articles you’ve read – you need to synthesize the literature to show how it all fits together (and how your own research fits in).

Synthesizing simply means combining. Instead of summarizing the main points of each source in turn, you put together the ideas and findings of multiple sources in order to make an overall point.

At the most basic level, this involves looking for similarities and differences between your sources. Your synthesis should show the reader where the sources overlap and where they diverge.

Unsynthesized Example

Franz (2008) studied undergraduate online students. He looked at 17 females and 18 males and found that none of them liked APA. According to Franz, the evidence suggested that all students are reluctant to learn citations style. Perez (2010) also studies undergraduate students. She looked at 42 females and 50 males and found that males were significantly more inclined to use citation software ( p < .05). Findings suggest that females might graduate sooner. Goldstein (2012) looked at British undergraduates. Among a sample of 50, all females, all confident in their abilities to cite and were eager to write their dissertations.

Synthesized Example

Studies of undergraduate students reveal conflicting conclusions regarding relationships between advanced scholarly study and citation efficacy. Although Franz (2008) found that no participants enjoyed learning citation style, Goldstein (2012) determined in a larger study that all participants watched felt comfortable citing sources, suggesting that variables among participant and control group populations must be examined more closely. Although Perez (2010) expanded on Franz’s original study with a larger, more diverse sample…

Step 1: Organize your sources

After collecting the relevant literature, you’ve got a lot of information to work through, and no clear idea of how it all fits together.

Before you can start writing, you need to organize your notes in a way that allows you to see the relationships between sources.

One way to begin synthesizing the literature is to put your notes into a table. Depending on your topic and the type of literature you’re dealing with, there are a couple of different ways you can organize this.

Summary table

A summary table collates the key points of each source under consistent headings. This is a good approach if your sources tend to have a similar structure – for instance, if they’re all empirical papers.

Each row in the table lists one source, and each column identifies a specific part of the source. You can decide which headings to include based on what’s most relevant to the literature you’re dealing with.

For example, you might include columns for things like aims, methods, variables, population, sample size, and conclusion.

For each study, you briefly summarize each of these aspects. You can also include columns for your own evaluation and analysis.

summary table for synthesizing the literature

The summary table gives you a quick overview of the key points of each source. This allows you to group sources by relevant similarities, as well as noticing important differences or contradictions in their findings.

Synthesis matrix

A synthesis matrix is useful when your sources are more varied in their purpose and structure – for example, when you’re dealing with books and essays making various different arguments about a topic.

Each column in the table lists one source. Each row is labeled with a specific concept, topic or theme that recurs across all or most of the sources.

Then, for each source, you summarize the main points or arguments related to the theme.

synthesis matrix

The purposes of the table is to identify the common points that connect the sources, as well as identifying points where they diverge or disagree.

Step 2: Outline your structure

Now you should have a clear overview of the main connections and differences between the sources you’ve read. Next, you need to decide how you’ll group them together and the order in which you’ll discuss them.

For shorter papers, your outline can just identify the focus of each paragraph; for longer papers, you might want to divide it into sections with headings.

There are a few different approaches you can take to help you structure your synthesis.

If your sources cover a broad time period, and you found patterns in how researchers approached the topic over time, you can organize your discussion chronologically .

That doesn’t mean you just summarize each paper in chronological order; instead, you should group articles into time periods and identify what they have in common, as well as signalling important turning points or developments in the literature.

If the literature covers various different topics, you can organize it thematically .

That means that each paragraph or section focuses on a specific theme and explains how that theme is approached in the literature.

synthesizing the literature using themes

Source Used with Permission: The Chicago School

If you’re drawing on literature from various different fields or they use a wide variety of research methods, you can organize your sources methodologically .

That means grouping together studies based on the type of research they did and discussing the findings that emerged from each method.

If your topic involves a debate between different schools of thought, you can organize it theoretically .

That means comparing the different theories that have been developed and grouping together papers based on the position or perspective they take on the topic, as well as evaluating which arguments are most convincing.

Step 3: Write paragraphs with topic sentences

What sets a synthesis apart from a summary is that it combines various sources. The easiest way to think about this is that each paragraph should discuss a few different sources, and you should be able to condense the overall point of the paragraph into one sentence.

This is called a topic sentence , and it usually appears at the start of the paragraph. The topic sentence signals what the whole paragraph is about; every sentence in the paragraph should be clearly related to it.

A topic sentence can be a simple summary of the paragraph’s content:

“Early research on [x] focused heavily on [y].”

For an effective synthesis, you can use topic sentences to link back to the previous paragraph, highlighting a point of debate or critique:

“Several scholars have pointed out the flaws in this approach.” “While recent research has attempted to address the problem, many of these studies have methodological flaws that limit their validity.”

By using topic sentences, you can ensure that your paragraphs are coherent and clearly show the connections between the articles you are discussing.

As you write your paragraphs, avoid quoting directly from sources: use your own words to explain the commonalities and differences that you found in the literature.

Don’t try to cover every single point from every single source – the key to synthesizing is to extract the most important and relevant information and combine it to give your reader an overall picture of the state of knowledge on your topic.

Step 4: Revise, edit and proofread

Like any other piece of academic writing, synthesizing literature doesn’t happen all in one go – it involves redrafting, revising, editing and proofreading your work.

Checklist for Synthesis

  •   Do I introduce the paragraph with a clear, focused topic sentence?
  •   Do I discuss more than one source in the paragraph?
  •   Do I mention only the most relevant findings, rather than describing every part of the studies?
  •   Do I discuss the similarities or differences between the sources, rather than summarizing each source in turn?
  •   Do I put the findings or arguments of the sources in my own words?
  •   Is the paragraph organized around a single idea?
  •   Is the paragraph directly relevant to my research question or topic?
  •   Is there a logical transition from this paragraph to the next one?

Further Information

How to Synthesise: a Step-by-Step Approach

Help…I”ve Been Asked to Synthesize!

Learn how to Synthesise (combine information from sources)

How to write a Psychology Essay

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Chapter 7: Synthesizing Sources

Learning objectives.

At the conclusion of this chapter, you will be able to:

  • synthesize key sources connecting them with the research question and topic area.

7.1 Overview of synthesizing

7.1.1 putting the pieces together.

Combining separate elements into a whole is the dictionary definition of synthesis.  It is a way to make connections among and between numerous and varied source materials.  A literature review is not an annotated bibliography, organized by title, author, or date of publication.  Rather, it is grouped by topic to create a whole view of the literature relevant to your research question.

analysis and synthesis in literature review

Your synthesis must demonstrate a critical analysis of the papers you collected as well as your ability to integrate the results of your analysis into your own literature review.  Each paper collected should be critically evaluated and weighed for “adequacy, appropriateness, and thoroughness” ( Garrard, 2017 ) before inclusion in your own review.  Papers that do not meet this criteria likely should not be included in your literature review.

Begin the synthesis process by creating a grid, table, or an outline where you will summarize, using common themes you have identified and the sources you have found. The summary grid or outline will help you compare and contrast the themes so you can see the relationships among them as well as areas where you may need to do more searching. Whichever method you choose, this type of organization will help you to both understand the information you find and structure the writing of your review.  Remember, although “the means of summarizing can vary, the key at this point is to make sure you understand what you’ve found and how it relates to your topic and research question” ( Bennard et al., 2014 ).

Figure 7.2 shows an example of a simplified literature summary table. In this example, individual journal citations are listed in rows. Table column headings read: purpose, methods, and results.

As you read through the material you gather, look for common themes as they may provide the structure for your literature review.  And, remember, research is an iterative process: it is not unusual to go back and search information sources for more material.

At one extreme, if you are claiming, ‘There are no prior publications on this topic,’ it is more likely that you have not found them yet and may need to broaden your search.  At another extreme, writing a complete literature review can be difficult with a well-trod topic.  Do not cite it all; instead cite what is most relevant.  If that still leaves too much to include, be sure to reference influential sources…as well as high-quality work that clearly connects to the points you make. ( Klingner, Scanlon, & Pressley, 2005 ).

7.2 Creating a summary table

Literature reviews can be organized sequentially or by topic, theme, method, results, theory, or argument.  It’s important to develop categories that are meaningful and relevant to your research question.  Take detailed notes on each article and use a consistent format for capturing all the information each article provides.  These notes and the summary table can be done manually, using note cards.  However, given the amount of information you will be recording, an electronic file created in a word processing or spreadsheet is more manageable. Examples of fields you may want to capture in your notes include:

  • Authors’ names
  • Article title
  • Publication year
  • Main purpose of the article
  • Methodology or research design
  • Participants
  • Measurement
  • Conclusions

  Other fields that will be useful when you begin to synthesize the sum total of your research:

  • Specific details of the article or research that are especially relevant to your study
  • Key terms and definitions
  • Strengths or weaknesses in research design
  • Relationships to other studies
  • Possible gaps in the research or literature (for example, many research articles conclude with the statement “more research is needed in this area”)
  • Finally, note how closely each article relates to your topic.  You may want to rank these as high, medium, or low relevance.  For papers that you decide not to include, you may want to note your reasoning for exclusion, such as ‘small sample size’, ‘local case study,’ or ‘lacks evidence to support assertion.’

This short video demonstrates how a nursing researcher might create a summary table.

7.2.1 Creating a Summary Table

analysis and synthesis in literature review

  Summary tables can be organized by author or by theme, for example:

Author/Year Research Design Participants or Population Studied Comparison Outcome
Smith/2010 Mixed methods Undergraduates Graduates Improved access
King/2016 Survey Females Males Increased representation
Miller/2011 Content analysis Nurses Doctors New procedure

For a summary table template, see http://blogs.monm.edu/writingatmc/files/2013/04/Synthesis-Matrix-Template.pdf

7.3 Creating a summary outline

An alternate way to organize your articles for synthesis it to create an outline. After you have collected the articles you intend to use (and have put aside the ones you won’t be using), it’s time to identify the conclusions that can be drawn from the articles as a group.

  Based on your review of the collected articles, group them by categories.  You may wish to further organize them by topic and then chronologically or alphabetically by author.  For each topic or subtopic you identified during your critical analysis of the paper, determine what those papers have in common.  Likewise, determine which ones in the group differ.  If there are contradictory findings, you may be able to identify methodological or theoretical differences that could account for the contradiction (for example, differences in population demographics).  Determine what general conclusions you can report about the topic or subtopic as the entire group of studies relate to it.  For example, you may have several studies that agree on outcome, such as ‘hands on learning is best for science in elementary school’ or that ‘continuing education is the best method for updating nursing certification.’ In that case, you may want to organize by methodology used in the studies rather than by outcome.

Organize your outline in a logical order and prepare to write the first draft of your literature review.  That order might be from broad to more specific, or it may be sequential or chronological, going from foundational literature to more current.  Remember, “an effective literature review need not denote the entire historical record, but rather establish the raison d’etre for the current study and in doing so cite that literature distinctly pertinent for theoretical, methodological, or empirical reasons.” ( Milardo, 2015, p. 22 ).

As you organize the summarized documents into a logical structure, you are also appraising and synthesizing complex information from multiple sources.  Your literature review is the result of your research that synthesizes new and old information and creates new knowledge.

7.4 Additional resources:

Literature Reviews: Using a Matrix to Organize Research / Saint Mary’s University of Minnesota

Literature Review: Synthesizing Multiple Sources / Indiana University

Writing a Literature Review and Using a Synthesis Matrix / Florida International University

 Sample Literature Reviews Grid / Complied by Lindsay Roberts

Select three or four articles on a single topic of interest to you. Then enter them into an outline or table in the categories you feel are important to a research question. Try both the grid and the outline if you can to see which suits you better. The attached grid contains the fields suggested in the video .

Literature Review Table  

Author

Date

Topic/Focus

Purpose

Conceptual

Theoretical Framework

Paradigm

Methods

Context

Setting

Sample

Findings Gaps

Test Yourself

  • Select two articles from your own summary table or outline and write a paragraph explaining how and why the sources relate to each other and your review of the literature.
  • In your literature review, under what topic or subtopic will you place the paragraph you just wrote?

Image attribution

Literature Reviews for Education and Nursing Graduate Students Copyright © by Linda Frederiksen is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Writing the Literature Review

  • Getting Started
  • Step 1: Choose A Topic
  • Step 2: Find Information
  • Step 3: Evaluate
  • Step 4: Take Notes
  • Step 5: Synthesize
  • Step 6: Stay Organized
  • Write the Review

Synthesizing

What is "Synthesis"?

analysis and synthesis in literature review

Synthesis?  

Synthesis refers to combining separate elements to create a whole.  When reading through your sources (peer reviewed journal articles, books, research studies, white papers etc.) you will pay attention to relationships between the studies, between groups in the studies, and look for any pattterns,  similarities or differences.  Pay attention to methodologies, unexplored themes, and things that may represent a "gap" in the literature.  These "gaps" will be things you will want to be sure to identify in your literature review.  

  • Using a Synthesis Matrix to Plan a Literature Review Introduction to synthesis matrices, and explanation of the difference between synthesis and analysis. (Geared towards Health Science/ Nursing but applicable for other literature reviews) ***Includes a synthesis matrix example***
  • Using a Spider Diagram Organize your thoughts with a spider diagram

Ready, Set...Synthesize

  • Create an outline that puts your topics (and subtopics) into a logical order
  • Look at each subtopic that you have identified and determine what the articles in that group have in common with each other
  • Look at the articles in those subtopics that you have identified and look for areas where they differ.
  • If you spot findings that are contradictory, what differences do you think could account for those contradictions?  
  • Determine what general conclusions can be reported about that subtopic, and how it relates to the group of studies that you are discussing
  • As you write, remember to follow your outline, and use transitions as you move between topics 

Galvan, J. L. (2006). Writing literature reviews (3rd ed.). Glendale, CA: Pyrczak Publishing

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What Synthesis Methodology Should I Use? A Review and Analysis of Approaches to Research Synthesis

Kara schick-makaroff.

1 Faculty of Nursing, University of Alberta, Edmonton, AB, Canada

Marjorie MacDonald

2 School of Nursing, University of Victoria, Victoria, BC, Canada

Marilyn Plummer

3 College of Nursing, Camosun College, Victoria, BC, Canada

Judy Burgess

4 Student Services, University Health Services, Victoria, BC, Canada

Wendy Neander

Associated data, additional file 1.

Types of Research SynthesisKey CharacteristicsPurposeMethodsProduct
CONVENTIONAL

“The integrative literature review is a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated” [ , p.356].

Integrative literature reviews include studies using diverse methodologies (i.e., experimental and non-experimental research, as well as qualitative research) in order to more fully understand a phenomenon of interest. It may also include theoretical and empirical literature.

Start by clearly identifying the problem that the review is addressing and the purpose of the review. There usually is not a specific research question, but rather a research purpose.

The quality of primary sources may be appraised using broad criteria. How quality is evaluated will depend upon the sampling frame .
Integrative reviews are used to address mature topics in order to re-conceptualize the expanding and diverse literature on the topic. They are also used to comprehensively review new topics in need of preliminary conceptualization .

Integrative reviews should ultimately present the “state of the art” of knowledge, depict the breadth and depth of the topic, and contribute to greater understanding of the phenomenon .
Integrative reviews generally contain similar steps , , which include the following: , is one overarching approach commonly used. Conclusions are often presented in a table/diagram. Explicit details from primary sources to support conclusions must be provided to demonstrate a logical chain of evidence.

Torraco suggests they can be represented in four forms:
Results should emphasize implications for policy/practice .
QUANTITATIVE

A SR is a review of literature that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyze data from the studies. Conducting a SR is analogous to conducting a primary study in that there are steps and protocols. It may or may not be done in conjunction with a meta-analysis.

In Cochrane , a SR is identified as the highest form of evidence in support of interventions. By contrast, the Joanna Briggs Institute does not define a SR as necessarily the highest form of evidence.

As noted below, a meta-analysis is always a SR, but a SR is not always a meta-analysis.

There is nothing that specifies data have to be quantitative, and the definition can apply to qualitative findings. Generally, however, the term has been used most frequently to apply to reviews of quantitative studies – traditional RCTs and experimental or quasi-experimental designs. More recently, both the Campbell and the Cochrane collaborations have been grappling with the need to, and the process of, integrating qualitative research into a SR. A number of studies have been published that do this , , , – .

A well-defined research question is required.

The Quality Appraisal section under MA above also applies to SR. Some researchers are developing standard reliable and valid quality appraisal tools to judge the quality of primary studies but there remains no consensus on which tools should be used. The Joanna Briggs Institute has developed their own criteria to ensure that only the highest quality studies are included in SRs for nursing, but they hold that studies from any methodological position are relevant.
The purpose of a SR is to integrate empirical research for the purpose of generalizing from a group of studies. The reviewer is also seeking to discover the limits of generalization .

Often, the review focuses on questions of intervention effectiveness. Thus, the intent is to summarize across studies to obtain a summative judgment about the effectiveness of interventions. However, the Joanna Briggs Institute suggests that for nursing, there is a concern not just with effectiveness but also with questions of appropriateness, meaningfulness and feasibility of health practices and delivery methods. Thus, SR's may have purposes other than to assess the effectiveness of interventions.
A number of authors have provided guidelines for conducting a SR but they generally contain similar steps: The products of a SR may include:
QUANTITATIVE

M-A is the statistical analysis of a large collection of results from individual studies (usually interventions) for the purposes of integrating the findings, based on conversion to a common metric (effect size) to determine the overall effect and its magnitude. The term was coined by Gene Glass – but dates back to 1904 . A M-A is always a SR (see above).

Data are from quantitative research studies and findings, primarily randomized control trials. Increasingly there is use of experimental, quasi-experimental and some types of observational studies. Each primary study is abstracted and coded into a database.

A clear, well-defined research question or hypothesis is required.

Articles are usually appraised according to a set of pre-defined criteria but these criteria vary considerably and there are many methodological limitations . Lower quality studies are not necessarily excluded and there is some debate about whether these should be included , . When lower quality studies are included, the validity of the findings is often discussed in relation to the study quality.
Analytic M-As are conducted for the purpose of summarizing and integrating the results of individual primary studies to increase the power for detecting intervention effects, which may be small and insignificant in the individual studies – .

Exploratory M-As are conducted to resolve controversy in a field or to pose and answer new questions. The main concern is to explain the variation in effect sizes.
Specific steps include : The product for M-A includes a narrative summary of the findings with a conclusion about the effectiveness of interventions.
QUALITATIVE

“Meta-study is a research approach involving analysis of the theory, methods, and findings of qualitative research and the synthesis of these insights into new ways of thinking about phenomenon” [ , p.1].

Three analytic components are undertaken prior to synthesis. Data includes qualitative findings (meta-data), research methods (meta-method), and/or philosophical/theoretical perspectives (meta-theory).

A relevant, well-defined research question is used.

According to Paterson et al. , primary articles are appraised according to specific criteria; however the specific appraisal will depend on the requirements of the meta-study. Studies of poor quality will be excluded. Data from included studies may also be excluded if reported themes are not supported by the presented data.
Analysis of research findings, methods, and theory across qualitative studies are compared and contrasted to create a new interpretation .Paterson et al. propose a clear set of techniques: Through the three meta-study processes, researchers create a “meta-synthesis” which brings together ideas to develop a mid-range theory as the product.
QUALITATIVE

Meta-ethnography entails choosing relevant empirical studies to synthesize through repetitive reading while noting metaphors – . Noblit and Hare explain that “metaphors” refer to “themes, perspectives, organizers, and/or concepts revealed by qualitative studies” [ , p.15]. These metaphors are then used as data for the synthesis through (at least) one of three strategies including reciprocal translation, refutational synthesis, and/or line of argument syntheses. A meta-ethnographic synthesis is the creation of interpretive (abstract) explanations that are essentially metaphoric. The goal is to create, in a reduced form, a representation of the abstraction through metaphor, all the while preserving the relationships between concepts .

Qualitative research studies and findings on a specific topic.

An “intellectual interest” [ , p.26] begins the process. Then, a relevant research question, aim, or purpose is developed.

Researchers are divided on the merits of critical appraisal and whether or not it should be a standard element in meta-ethnography . Some researchers choose to follow pre-determined criteria based on critical appraisal [e.g., ], whereas others do not critically appraise.
To synthesize qualitative studies through a building of “comparative understanding” [ , p.22] so that the result is greater than the sum of the parts.

Noblit and Hare summarize that meta-ethnography is “a form of synthesis for ethnographic or other interpretive studies. It enables us to talk to each other about our studies; to communicate to policy makers, concerned citizens, and scholars what interpretive research reveals; and to reflect on our collective craft and the place of our own studies within it” [ , p.14].
Methods used in meta-ethnography generally following the following: .

Noblit and Hare identified three possible analysis strategies (all do not have to be completed):
The product of a meta-ethnography is a mid-range theory that has greater explanatory power than could be otherwise achieved in a conventional literature review.
QUALITATIVE

A grounded formal theory (GFT) is a synthesis of substantive grounded theories (GTs) to produce a higher order, more abstract theory that goes beyond the specifics of the original theories. GFT takes into account the conditions under which the primary study data were collected and analyzed to develop a more generalized and abstract model .

Substantive GTs were originally constructed using the methodology developed by Glaser & Strauss . While some synthesis approaches emphasize including all possible primary GT studies, the concept of saturation in GFT (see Methods column) allows limiting the number of reviewed papers to emphasize robustness rather than completeness .

GFT begins with a phenomenon of focus . Analytic questions and the overall research question emerge throughout the process.

There is no discussion in the GFT literature about critically appraising the studies to be included. However, the nature of the analytic process suggests that critical appraisal may not be relevant. The authenticity and accuracy of data in a GFT are not an issue because, for the purposes of generating theory, what is important is the conceptual category and not the accuracy of the evidence. The constant comparative method of GFT will correct for such inaccuracies because each concept must “earn” its way into the theory by repeatedly showing up – .
The intent of GFT is to expand the applicability of individual GTs by synthesizing the findings to provide a broad meaning that is based in data and is applicable to people who experience a common phenomenon across populations and context .

The focus is on the conditions under which theoretical generalizations apply. GFT aims “to bring cultural and individual differences into dialogue with each other by seeking a metaphor through which those differences can be understood by others” [ , p.1354].
GFT uses the same methods that were used to create the original GTs in the synthesis , . Specific elements of the analytic process include: , . A GFT is a mid-range GT that has “fit, work and grab”: that is, it fits the data (concepts and categories from primary studies), works to explain the phenomenon under review, and resonates with the readers' experiences and understandings.

Thorne et al. suggest that a GFT is “an artistic explanation that works for now, a model created on the basis of limited materials and a specific, situated perspective within known and unconscious limits of representation” [ , p.1354].
QUALITATIVE

Concept analysis is a systematic procedure to extract attributes of a concept from literature, definitions and case examples to delineate the meaning of that concept with respect to a certain domain or context.

Most writings on concept analysis do not specify the data type. However, our scan of the methodological and empirical literature on concept analysis suggests that although the analytic approach in concept analysis is qualitative, quantitative study designs and data can be used to address the questions related to defining the meaning of a concept [e.g. , – ].

Requires the researcher to isolate or identify a conceptual question or concept of interest.

Quality appraisal is not typically attended to in concept analyses. Rather, researchers are interested in all instances of actual use of a concept (or surrogate terms) .
Concept analysis is used to extend the theoretical meaning of a concept or to understand a conceptual practice problem – . In this case, concepts are cognitive descriptive meanings utilized for theoretical or practical purposes.

Concept analysis is used to identify, clarify, and refine or define the meaning of a concept and can be used as a first step in theory development , .
There are varied procedural techniques attributed to various authors such as Wilson , Walker & Avant , Chinn & (Jacobs) Kramer – , Rodgers & Knafl, , Rodgers , Schwartz-Barcott & Kim , and Morse .

Despite varied techniques, steps generally include: , , .
Concept analysis generates a definition of a concept that may be used to operationalize phenomena for further research study or theory development .
EMERGING

Although no universal definition exists, there are some common elements of scoping reviews , . They are exploratory projects that systematically map the literature on a topic, identifying the key concepts, theories, sources of evidence, and gaps in the research. It involves systematically selecting, collecting and summarizing knowledge in a broad area .

A scoping review is used to address broad topics where many different study designs and methods might be applicable. It may be conducted as part of an ongoing review, or as a stand-alone summary of research. Whereas a systematic review assesses a narrow range of quality-assessed studies to synthesize or aggregate findings, a scoping review assesses a much broader range of literature with a wide focus and does not synthesize or aggregate the findings .

Includes studies using any data type or method. May include empirical, theoretical or conceptual papers. Exclusion and inclusion criteria are inductively derived and based on relevance rather than on the quality of the primary studies or articles .

The question is stated broadly and often becomes refined as the study progresses. One or more general questions may guide the review.

The scoping review does not provide an appraisal of the quality of the evidence. It presents the existing literature without weighting the evidence in relation to specific interventions.
The purpose of a scoping review is to examine the extent, range and nature of research activity in an area. It is done to identify where there is sufficient evidence to conduct a full synthesis or to determine that insufficient evidence exists and additional primary research is needed , . It may be done for the purpose of disseminating research findings or to clarify working definitions and the conceptual boundaries of a topic area .Arksey and O'Malley recommend a 5 step process for conducting a scoping review:
More recently, Levac et al. have proposed recommendations to clarify and enhance each stage of the framework described above.
The product of a scoping review will depend on the purpose for which it is conducted. In general, however, the narrative report provides an overview of all reviewed material.

The product generally includes:
EMERGING

? Rapid review of the literature provides a quick, rather than comprehensive, overview of the literature on a narrowly defined issue. Rapid review evolved out of a need to inform policy makers about issues and interventions in a timely manner . It is often proposed as an intermediary step to be followed by a more comprehensive review.

The literature is often narrowly defined, focusing on a specific issue or a specific local, regional, or federal context . It can include diverse study designs, methods, and data types as well as peer reviewed and gray literature.

Rapid reviews require a thorough understanding of the intended audience and a specific, focused research question.

Rapid reviews typically do not include an assessment of the quality of the literature, nor do they always include the views of experts and/or reviews by peers .
The purpose is to produce a fast review of the literature, within a defined and usually limited time frame, on a question of immediate importance to a stakeholder group.There is no standardized methodology as yet, but the depth and breadth of the review depends upon the specific purpose and the allotted time frame. Rapid reviews typically take one to nine months. – . – . .

It is important that those conducting a rapid review describe the methodology in detail to promote transparency, support transferability, and avoid misrepresenting the veracity of the findings .
Typically a concise report is written for macro-level decision-makers that answer the specific review question.
EMERGING

MNS is a new form of systematic review that addresses the issues of synthesizing a large and complex body of data from diverse and heterogeneous sources. At the same time, it is systematic in that it is conducted “according to an explicit, rigorous and transparent method” [ , p.418].

The approach moves from logico-scientific reasoning (which underlies many approaches to synthesis) to narrative-interpretive reasoning. The unit of analysis for the synthesis is the unfolding “storyline” of a research tradition over time. Five key principles underlie the methodology: pragmatism, pluralism, historicity, contestation, and peer review.

This methodology involves the judicious combination of qualitative and quantitative evidence, and the theoretical and empirical literature.

: The original research question is outlined in a broad, open-ended format, and may shift and change through the process.

MNS uses the criteria of the research tradition of the primary study to judge the quality of the research, generally as set out in key sources within that tradition.
The purpose is to summarize, synthesize and interpret a diverse body of literature from multiple traditions that use different methods, theoretical perspectives, and data types.The steps to conduct a MNS , – include the following: The product of a MNS is:
EMERGING

? A realist synthesis is a review of complex social interventions and programs that seek to unpack the mechanisms by which complex programs produce outcomes, and the context in which the relationship occurs. This is in contrast to systematic reviews, which aim to synthesize studies on whether interventions are effective. Realist synthesis seeks to answer the question: What works for whom, in what ways and under what circumstances?

This form of synthesis represents a review logic not a review technique . Instead of a replicable method that follows rigid rules, the logic of realist review is based on principles. It reflects a shift away from an ontology of empirical realism to one of critical realism .

There is no specific data preference but will include quantitative, qualitative and grey literature. Because the focus is on the mechanisms of action and their context, seemingly disparate bodies of literature and diverse methodologies are included. The focus is upon literature that emphasizes process with detailed descriptions of the interventions and context.

The review question is carefully articulated, prioritizing different aspects of an intervention . It can be a broad question.

Realist review supports the principle that high quality evidence should be used but takes a different position than in systematic reviews on how the evidence is to be judged. It rejects a hierarchical approach to quality because multiple methods are needed to identify all aspects of the context, mechanisms and outcomes. Appraisal checklists are viewed skeptically because they cannot be applied evenly across the diverse study types and methods being reviewed. Thus, quality appraisal is seen as occurring in stages with a focus on the relevance of the study or article to the theory under consideration, and the extent to which an inference drawn has sufficient weight to make a credible contribution to the test of a particular intervention theory .
The purpose of a realist synthesis is to guide program and policy development by providing decision makers with a set of program theories that identify potential policy levers for change. Within its explanatory intent, there are four general purposes: , ].Pawson et al. identify 5 steps: Pawson explains that realist synthesis ends up with useful, middle-range theory. However, the product of a realist review combines theoretical understanding with empirical evidence. It focuses on explaining the relationships among the context in which an intervention takes place, the mechanisms by which it works, and the outcomes produced – .
Recommendations for dissemination and implementation are explicitly articulated. The result is a series of contextualized decision points that describe the contingencies of effectiveness. That is, a realist review provides an explanatory analysis that answers the original question of “what works for whom, in what circumstances, in what respects, and how” [ , p.21].
EMERGING

CIS is a methodology with an explicit orientation to theory generation, developed to respond to the need identified in the literature for rigorous methods to synthesize diverse types of research evidence generated by diverse methodologies particularly when the body of evidence is very complex . Thus, it was developed to address the limitations of conventional systematic review techniques. It involves an iterative process and recognizes the need for flexibility and reflexivity. It addresses the criticism that many approaches to syntheses are insufficiently critical and do not question the epistemological and normative assumptions reflected in the literature . CIS is “sensitized to the kinds of processes involved in a conventional systematic review while drawing on a distinctively qualitative tradition of inquiry” [ , p.35].

CIS utilizes data from quantitative and qualitative empirical studies, conceptual and theoretical papers, reviews and commentaries.

It is neither possible nor desirable to specify a precise review question in advance. Rather the process is highly iterative and may not be finalized until the end of the review. There is no hierarchy of designs for determining the quality of qualitative studies and, furthermore, no consensus exists on whether qualitative studies should even be assessed for quality . Studies for inclusion are not selected on the basis of study design or methodological quality. Rather, papers that are relevant are prioritized. However, papers that are determined to be fatally flawed are excluded on the basis of a set of questions for determining quality [see ]. Often, however, judgments about quality are deferred until the synthesis phase because even methodologically weak papers can provide important theoretical or conceptual insights .
The purpose of CIS is to develop an in-depth understanding of an issue/research question “by drawing on broadly relevant literature to develop concepts and theories that integrate those concepts” [ , p.71]. The overarching aim is to generate theory.The developers of CIS explicitly reject a staged approach to the review. Rather, the processes are iterative, interactive, dynamic and recursive. It includes these general categories of activities – : The product is a “synthesizing argument” that “links existing constructions from the findings to ‘synthetic constructs' (new constructs generated through synthesis)” [ , p.71]. The synthesizing argument integrates evidence from across the studies in the review into a coherent theoretical framework – . This may be represented as a “conceptual map” that identifies the main synthetic constructs and illustrates the relationships among them .

When we began this process, we were doctoral students and a faculty member in a research methods course. As students, we were facing a review of the literature for our dissertations. We encountered several different ways of conducting a review but were unable to locate any resources that synthesized all of the various synthesis methodologies. Our purpose is to present a comprehensive overview and assessment of the main approaches to research synthesis. We use ‘research synthesis’ as a broad overarching term to describe various approaches to combining, integrating, and synthesizing research findings.

We conducted an integrative review of the literature to explore the historical, contextual, and evolving nature of research synthesis. We searched five databases, reviewed websites of key organizations, hand-searched several journals, and examined relevant texts from the reference lists of the documents we had already obtained.

We identified four broad categories of research synthesis methodology including conventional, quantitative, qualitative, and emerging syntheses. Each of the broad categories was compared to the others on the following: key characteristics, purpose, method, product, context, underlying assumptions, unit of analysis, strengths and limitations, and when to use each approach.

Conclusions

The current state of research synthesis reflects significant advancements in emerging synthesis studies that integrate diverse data types and sources. New approaches to research synthesis provide a much broader range of review alternatives available to health and social science students and researchers.

1. Introduction

Since the turn of the century, public health emergencies have been identified worldwide, particularly related to infectious diseases. For example, the Severe Acute Respiratory Syndrome (SARS) epidemic in Canada in 2002-2003, the recent Ebola epidemic in Africa, and the ongoing HIV/AIDs pandemic are global health concerns. There have also been dramatic increases in the prevalence of chronic diseases around the world [1] – [3] . These epidemiological challenges have raised concerns about the ability of health systems worldwide to address these crises. As a result, public health systems reform has been initiated in a number of countries. In Canada, as in other countries, the role of evidence to support public health reform and improve population health has been given high priority. Yet, there continues to be a significant gap between the production of evidence through research and its application in practice [4] – [5] . One strategy to address this gap has been the development of new research synthesis methodologies to deal with the time-sensitive and wide ranging evidence needs of policy makers and practitioners in all areas of health care, including public health.

As doctoral nursing students facing a review of the literature for our dissertations, and as a faculty member teaching a research methods course, we encountered several ways of conducting a research synthesis but found no comprehensive resources that discussed, compared, and contrasted various synthesis methodologies on their purposes, processes, strengths and limitations. To complicate matters, writers use terms interchangeably or use different terms to mean the same thing, and the literature is often contradictory about various approaches. Some texts [6] , [7] – [9] did provide a preliminary understanding about how research synthesis had been taken up in nursing, but these did not meet our requirements. Thus, in this article we address the need for a comprehensive overview of research synthesis methodologies to guide public health, health care, and social science researchers and practitioners.

Research synthesis is relatively new in public health but has a long history in other fields dating back to the late 1800s. Research synthesis, a research process in its own right [10] , has become more prominent in the wake of the evidence-based movement of the 1990s. Research syntheses have found their advocates and detractors in all disciplines, with challenges to the processes of systematic review and meta-analysis, in particular, being raised by critics of evidence-based healthcare [11] – [13] .

Our purpose was to conduct an integrative review of the literature to explore the historical, contextual, and evolving nature of research synthesis [14] – [15] . We synthesize and critique the main approaches to research synthesis that are relevant for public health, health care, and social scientists. Research synthesis is the overarching term we use to describe approaches to combining, aggregating, integrating, and synthesizing primary research findings. Each synthesis methodology draws on different types of findings depending on the purpose and product of the chosen synthesis (see Additional File 1 ).

3. Method of Review

Based on our current knowledge of the literature, we identified these approaches to include in our review: systematic review, meta-analysis, qualitative meta-synthesis, meta-narrative synthesis, scoping review, rapid review, realist synthesis, concept analysis, literature review, and integrative review. Our first step was to divide the synthesis types among the research team. Each member did a preliminary search to identify key texts. The team then met to develop search terms and a framework to guide the review.

Over the period of 2008 to 2012 we extensively searched the literature, updating our search at several time points, not restricting our search by date. The dates of texts reviewed range from 1967 to 2015. We used the terms above combined with the term “method* (e.g., “realist synthesis” and “method*) in the database Health Source: Academic Edition (includes Medline and CINAHL). This search yielded very few texts on some methodologies and many on others. We realized that many documents on research synthesis had not been picked up in the search. Therefore, we also searched Google Scholar, PubMed, ERIC, and Social Science Index, as well as the websites of key organizations such as the Joanna Briggs Institute, the University of York Centre for Evidence-Based Nursing, and the Cochrane Collaboration database. We hand searched several nursing, social science, public health and health policy journals. Finally, we traced relevant documents from the references in obtained texts.

We included works that met the following inclusion criteria: (1) published in English; (2) discussed the history of research synthesis; (3) explicitly described the approach and specific methods; or (4) identified issues, challenges, strengths and limitations of the particular methodology. We excluded research reports that resulted from the use of particular synthesis methodologies unless they also included criteria 2, 3, or 4 above.

Based on our search, we identified additional types of research synthesis (e.g., meta-interpretation, best evidence synthesis, critical interpretive synthesis, meta-summary, grounded formal theory). Still, we missed some important developments in meta-analysis, for example, identified by the journal's reviewers that have now been discussed briefly in the paper. The final set of 197 texts included in our review comprised theoretical, empirical, and conceptual papers, books, editorials and commentaries, and policy documents.

In our preliminary review of key texts, the team inductively developed a framework of the important elements of each method for comparison. In the next phase, each text was read carefully, and data for these elements were extracted into a table for comparison on the points of: key characteristics, purpose, methods, and product; see Additional File 1 ). Once the data were grouped and extracted, we synthesized across categories based on the following additional points of comparison: complexity of the process, degree of systematization, consideration of context, underlying assumptions, unit of analysis, and when to use each approach. In our results, we discuss our comparison of the various synthesis approaches on the elements above. Drawing only on documents for the review, ethics approval was not required.

We identified four broad categories of research synthesis methodology: Conventional, quantitative, qualitative, and emerging syntheses. From our dataset of 197 texts, we had 14 texts on conventional synthesis, 64 on quantitative synthesis, 78 on qualitative synthesis, and 41 on emerging syntheses. Table 1 provides an overview of the four types of research synthesis, definitions, types of data used, products, and examples of the methodology.

Types of Research SynthesisDefinitionData Types UsedProductsExamples
1. Conventional SynthesisOlder forms of review with less-systematic examination, critique, and synthesis of the literature on a mature topic for re-conceptulization or on a new topic for preliminary conceptualization , –
2. Quantitative SynthesisCombining, aggregating, or integrating quantitative empirical research with data expressed in numeric form , – – –
3. Qualitative SynthesisCombining, aggregating, or integrating qualitative empirical research and/or theoretical work expressed in narrative form – – , – , , – , – – , – – , –
4. Emerging SynthesisNewer syntheses that provide a systematic approach to synthesizing varied literature in a topic area that includes diverse data types – – – – , , –

Although we group these types of synthesis into four broad categories on the basis of similarities, each type within a category has unique characteristics, which may differ from the overall group similarities. Each could be explored in greater depth to tease out their unique characteristics, but detailed comparison is beyond the scope of this article.

Additional File 1 presents one or more selected types of synthesis that represent the broad category but is not an exhaustive presentation of all types within each category. It provides more depth for specific examples from each category of synthesis on the characteristics, purpose, methods, and products than is found in Table 1 .

4.1. Key Characteristics

4.1.1. what is it.

Here we draw on two types of categorization. First, we utilize Dixon Woods et al.'s [49] classification of research syntheses as being either integrative or interpretive . (Please note that integrative syntheses are not the same as an integrative review as defined in Additional File 1 .) Second, we use Popay's [80] enhancement and epistemological models .

The defining characteristics of integrative syntheses are that they involve summarizing the data achieved by pooling data [49] . Integrative syntheses include systematic reviews, meta-analyses, as well as scoping and rapid reviews because each of these focus on summarizing data. They also define concepts from the outset (although this may not always be true in scoping or rapid reviews) and deal with a well-specified phenomenon of interest.

Interpretive syntheses are primarily concerned with the development of concepts and theories that integrate concepts [49] . The analysis in interpretive synthesis is conceptual both in process and outcome, and “the product is not aggregations of data, but theory” [49] , [p.12]. Interpretive syntheses involve induction and interpretation, and are primarily conceptual in process and outcome. Examples include integrative reviews, some systematic reviews, all of the qualitative syntheses, meta-narrative, realist and critical interpretive syntheses. Of note, both quantitative and qualitative studies can be either integrative or interpretive

The second categorization, enhancement versus epistemological , applies to those approaches that use multiple data types and sources [80] . Popay's [80] classification reflects the ways that qualitative data are valued in relation to quantitative data.

In the enhancement model , qualitative data adds something to quantitative analysis. The enhancement model is reflected in systematic reviews and meta-analyses that use some qualitative data to enhance interpretation and explanation. It may also be reflected in some rapid reviews that draw on quantitative data but use some qualitative data.

The epistemological model assumes that quantitative and qualitative data are equal and each has something unique to contribute. All of the other review approaches, except pure quantitative or qualitative syntheses, reflect the epistemological model because they value all data types equally but see them as contributing different understandings.

4.1.2. Data type

By and large, the quantitative approaches (quantitative systematic review and meta-analysis) have typically used purely quantitative data (i.e., expressed in numeric form). More recently, both Cochrane [81] and Campbell [82] collaborations are grappling with the need to, and the process of, integrating qualitative research into a systematic review. The qualitative approaches use qualitative data (i.e., expressed in words). All of the emerging synthesis types, as well as the conventional integrative review, incorporate qualitative and quantitative study designs and data.

4.1.3. Research question

Four types of research questions direct inquiry across the different types of syntheses. The first is a well-developed research question that gives direction to the synthesis (e.g., meta-analysis, systematic review, meta-study, concept analysis, rapid review, realist synthesis). The second begins as a broad general question that evolves and becomes more refined over the course of the synthesis (e.g., meta-ethnography, scoping review, meta-narrative, critical interpretive synthesis). In the third type, the synthesis begins with a phenomenon of interest and the question emerges in the analytic process (e.g., grounded formal theory). Lastly, there is no clear question, but rather a general review purpose (e.g., integrative review). Thus, the requirement for a well-defined question cuts across at least three of the synthesis types (e.g., quantitative, qualitative, and emerging).

4.1.4. Quality appraisal

This is a contested issue within and between the four synthesis categories. There are strong proponents of quality appraisal in the quantitative traditions of systematic review and meta-analysis based on the need for strong studies that will not jeopardize validity of the overall findings. Nonetheless, there is no consensus on pre-defined criteria; many scales exist that vary dramatically in composition. This has methodological implications for the credibility of findings [83] .

Specific methodologies from the conventional, qualitative, and emerging categories support quality appraisal but do so with caveats. In conventional integrative reviews appraisal is recommended, but depends on the sampling frame used in the study [18] . In meta-study, appraisal criteria are explicit but quality criteria are used in different ways depending on the specific requirements of the inquiry [54] . Among the emerging syntheses, meta-narrative review developers support appraisal of a study based on criteria from the research tradition of the primary study [67] , [84] – [85] . Realist synthesis similarly supports the use of high quality evidence, but appraisal checklists are viewed with scepticism and evidence is judged based on relevance to the research question and whether a credible inference may be drawn [69] . Like realist, critical interpretive syntheses do not judge quality using standardized appraisal instruments. They will exclude fatally flawed studies, but there is no consensus on what ‘fatally flawed’ means [49] , [71] . Appraisal is based on relevance to the inquiry, not rigor of the study.

There is no agreement on quality appraisal among qualitative meta-ethnographers with some supporting and others refuting the need for appraisal. [60] , [62] . Opponents of quality appraisal are found among authors of qualitative (grounded formal theory and concept analysis) and emerging syntheses (scoping and rapid reviews) because quality is not deemed relevant to the intention of the synthesis; the studies being reviewed are not effectiveness studies where quality is extremely important. These qualitative synthesis are often reviews of theoretical developments where the concept itself is what is important, or reviews that provide quotations from the raw data so readers can make their own judgements about the relevance and utility of the data. For example, in formal grounded theory, the purpose of theory generation and authenticity of data used to generate the theory is not as important as the conceptual category. Inaccuracies may be corrected in other ways, such as using the constant comparative method, which facilitates development of theoretical concepts that are repeatedly found in the data [86] – [87] . For pragmatic reasons, evidence is not assessed in rapid and scoping reviews, in part to produce a timely product. The issue of quality appraisal is unresolved across the terrain of research synthesis and we consider this further in our discussion.

4.2. Purpose

All research syntheses share a common purpose -- to summarize, synthesize, or integrate research findings from diverse studies. This helps readers stay abreast of the burgeoning literature in a field. Our discussion here is at the level of the four categories of synthesis. Beginning with conventional literature syntheses, the overall purpose is to attend to mature topics for the purpose of re-conceptualization or to new topics requiring preliminary conceptualization [14] . Such syntheses may be helpful to consider contradictory evidence, map shifting trends in the study of a phenomenon, and describe the emergence of research in diverse fields [14] . The purpose here is to set the stage for a study by identifying what has been done, gaps in the literature, important research questions, or to develop a conceptual framework to guide data collection and analysis.

The purpose of quantitative systematic reviews is to combine, aggregate, or integrate empirical research to be able to generalize from a group of studies and determine the limits of generalization [27] . The focus of quantitative systematic reviews has been primarily on aggregating the results of studies evaluating the effectiveness of interventions using experimental, quasi-experimental, and more recently, observational designs. Systematic reviews can be done with or without quantitative meta-analysis but a meta-analysis always takes place within the context of a systematic review. Researchers must consider the review's purpose and the nature of their data in undertaking a quantitative synthesis; this will assist in determining the approach.

The purpose of qualitative syntheses is broadly to synthesize complex health experiences, practices, or concepts arising in healthcare environments. There may be various purposes depending on the qualitative methodology. For example, in hermeneutic studies the aim may be holistic explanation or understanding of a phenomenon [42] , which is deepened by integrating the findings from multiple studies. In grounded formal theory, the aim is to produce a conceptual framework or theory expected to be applicable beyond the original study. Although not able to generalize from qualitative research in the statistical sense [88] , qualitative researchers usually do want to say something about the applicability of their synthesis to other settings or phenomena. This notion of ‘theoretical generalization’ has been referred to as ‘transferability’ [89] – [90] and is an important criterion of rigour in qualitative research. It applies equally to the products of a qualitative synthesis in which the synthesis of multiple studies on the same phenomenon strengthens the ability to draw transferable conclusions.

The overarching purpose of emerging syntheses is challenging the more traditional types of syntheses, in part by using data from both quantitative and qualitative studies with diverse designs for analysis. Beyond this, however, each emerging synthesis methodology has a unique purpose. In meta-narrative review, the purpose is to identify different research traditions in the area, synthesize a complex and diverse body of research. Critical interpretive synthesis shares this characteristic. Although a distinctive approach, critical interpretive synthesis utilizes a modification of the analytic strategies of meta-ethnography [61] (e.g., reciprocal translational analysis, refutational synthesis, and lines of argument synthesis) but goes beyond the use of these to bring a critical perspective to bear in challenging the normative or epistemological assumptions in the primary literature [72] – [73] . The unique purpose of a realist synthesis is to amalgamate complex empirical evidence and theoretical understandings within a diverse body of literature to uncover the operative mechanisms and contexts that affect the outcomes of social interventions. In a scoping review, the intention is to find key concepts, examine the range of research in an area, and identify gaps in the literature. The purpose of a rapid review is comparable to that of a scoping review, but done quickly to meet the time-sensitive information needs of policy makers.

4.3. Method

4.3.1. degree of systematization.

There are varying degrees of systematization across the categories of research synthesis. The most systematized are quantitative systematic reviews and meta-analyses. There are clear processes in each with judgments to be made at each step, although there are no agreed upon guidelines for this. The process is inherently subjective despite attempts to develop objective and systematic processes [91] – [92] . Mullen and Ramirez [27] suggest that there is often a false sense of rigour implied by the terms ‘systematic review’ and ‘meta-analysis’ because of their clearly defined procedures.

In comparison with some types of qualitative synthesis, concept analysis is quite procedural. Qualitative meta-synthesis also has defined procedures and is systematic, yet perhaps less so than concept analysis. Qualitative meta-synthesis starts in an unsystematic way but becomes more systematic as it unfolds. Procedures and frameworks exist for some of the emerging types of synthesis [e.g., [50] , [63] , [71] , [93] ] but are not linear, have considerable flexibility, and are often messy with emergent processes [85] . Conventional literature reviews tend not to be as systematic as the other three types. In fact, the lack of systematization in conventional literature synthesis was the reason for the development of more systematic quantitative [17] , [20] and qualitative [45] – [46] , [61] approaches. Some authors in the field [18] have clarified processes for integrative reviews making them more systematic and rigorous, but most conventional syntheses remain relatively unsystematic in comparison with other types.

4.3.2. Complexity of the process

Some synthesis processes are considerably more complex than others. Methodologies with clearly defined steps are arguably less complex than the more flexible and emergent ones. We know that any study encounters challenges and it is rare that a pre-determined research protocol can be followed exactly as intended. Not even the rigorous methods associated with Cochrane [81] systematic reviews and meta-analyses are always implemented exactly as intended. Even when dealing with numbers rather than words, interpretation is always part of the process. Our collective experience suggests that new methodologies (e.g., meta-narrative synthesis and realist synthesis) that integrate different data types and methods are more complex than conventional reviews or the rapid and scoping reviews.

4.4. Product

The products of research syntheses usually take three distinct formats (see Table 1 and Additional File 1 for further details). The first representation is in tables, charts, graphical displays, diagrams and maps as seen in integrative, scoping and rapid reviews, meta-analyses, and critical interpretive syntheses. The second type of synthesis product is the use of mathematical scores. Summary statements of effectiveness are mathematically displayed in meta-analyses (as an effect size), systematic reviews, and rapid reviews (statistical significance).

The third synthesis product may be a theory or theoretical framework. A mid-range theory can be produced from formal grounded theory, meta-study, meta-ethnography, and realist synthesis. Theoretical/conceptual frameworks or conceptual maps may be created in meta-narrative and critical interpretive syntheses, and integrative reviews. Concepts for use within theories are produced in concept analysis. While these three product types span the categories of research synthesis, narrative description and summary is used to present the products resulting from all methodologies.

4.5. Consideration of context

There are diverse ways that context is considered in the four broad categories of synthesis. Context may be considered to the extent that it features within primary studies for the purpose of the review. Context may also be understood as an integral aspect of both the phenomenon under study and the synthesis methodology (e.g., realist synthesis). Quantitative systematic reviews and meta-analyses have typically been conducted on studies using experimental and quasi-experimental designs and more recently observational studies, which control for contextual features to allow for understanding of the ‘true’ effect of the intervention [94] .

More recently, systematic reviews have included covariates or mediating variables (i.e., contextual factors) to help explain variability in the results across studies [27] . Context, however, is usually handled in the narrative discussion of findings rather than in the synthesis itself. This lack of attention to context has been one criticism leveled against systematic reviews and meta-analyses, which restrict the types of research designs that are considered [e.g., [95] ].

When conventional literature reviews incorporate studies that deal with context, there is a place for considering contextual influences on the intervention or phenomenon. Reviews of quantitative experimental studies tend to be devoid of contextual considerations since the original studies are similarly devoid, but context might figure prominently in a literature review that incorporates both quantitative and qualitative studies.

Qualitative syntheses have been conducted on the contextual features of a particular phenomenon [33] . Paterson et al. [54] advise researchers to attend to how context may have influenced the findings of particular primary studies. In qualitative analysis, contextual features may form categories by which the data can be compared and contrasted to facilitate interpretation. Because qualitative research is often conducted to understand a phenomenon as a whole, context may be a focus, although this varies with the qualitative methodology. At the same time, the findings in a qualitative synthesis are abstracted from the original reports and taken to a higher level of conceptualization, thus removing them from the original context.

Meta-narrative synthesis [67] , [84] , because it draws on diverse research traditions and methodologies, may incorporate context into the analysis and findings. There is not, however, an explicit step in the process that directs the analyst to consider context. Generally, the research question guiding the synthesis is an important factor in whether context will be a focus.

More recent iterations of concept analysis [47] , [96] – [97] explicitly consider context reflecting the assumption that a concept's meaning is determined by its context. Morse [47] points out, however, that Wilson's [98] approach to concept analysis, and those based on Wilson [e.g., [45] ], identify attributes that are devoid of context, while Rodgers' [96] , [99] evolutionary method considers context (e.g., antecedents, consequences, and relationships to other concepts) in concept development.

Realist synthesis [69] considers context as integral to the study. It draws on a critical realist logic of inquiry grounded in the work of Bhaskar [100] , who argues that empirical co-occurrence of events is insufficient for inferring causation. One must identify generative mechanisms whose properties are causal and, depending on the situation, may nor may not be activated [94] . Context interacts with program/intervention elements and thus cannot be differentiated from the phenomenon [69] . This approach synthesizes evidence on generative mechanisms and analyzes contextual features that activate them; the result feeds back into the context. The focus is on what works, for whom, under what conditions, why and how [68] .

4.6. Underlying Philosophical and Theoretical Assumptions

When we began our review, we ‘assumed’ that the assumptions underlying synthesis methodologies would be a distinguishing characteristic of synthesis types, and that we could compare the various types on their assumptions, explicit or implicit. We found, however, that many authors did not explicate the underlying assumptions of their methodologies, and it was difficult to infer them. Kirkevold [101] has argued that integrative reviews need to be carried out from an explicit philosophical or theoretical perspective. We argue this should be true for all types of synthesis.

Authors of some emerging synthesis approaches have been very explicit about their assumptions and philosophical underpinnings. An implicit assumption of most emerging synthesis methodologies is that quantitative systematic reviews and meta-analyses have limited utility in some fields [e.g., in public health – [13] , [102] ] and for some kinds of review questions like those about feasibility and appropriateness versus effectiveness [103] – [104] . They also assume that ontologically and epistemologically, both kinds of data can be combined. This is a significant debate in the literature because it is about the commensurability of overarching paradigms [105] but this is beyond the scope of this review.

Realist synthesis is philosophically grounded in critical realism or, as noted above, a realist logic of inquiry [93] , [99] , [106] – [107] . Key assumptions regarding the nature of interventions that inform critical realism have been described above in the section on context. See Pawson et al. [106] for more information on critical realism, the philosophical basis of realist synthesis.

Meta-narrative synthesis is explicitly rooted in a constructivist philosophy of science [108] in which knowledge is socially constructed rather than discovered, and what we take to be ‘truth’ is a matter of perspective. Reality has a pluralistic and plastic character, and there is no pre-existing ‘real world’ independent of human construction and language [109] . See Greenhalgh et al. [67] , [85] and Greenhalgh & Wong [97] for more discussion of the constructivist basis of meta-narrative synthesis.

In the case of purely quantitative or qualitative syntheses, it may be an easier matter to uncover unstated assumptions because they are likely to be shared with those of the primary studies in the genre. For example, grounded formal theory shares the philosophical and theoretical underpinnings of grounded theory, rooted in the theoretical perspective of symbolic interactionism [110] – [111] and the philosophy of pragmatism [87] , [112] – [114] .

As with meta-narrative synthesis, meta-study developers identify constructivism as their interpretive philosophical foundation [54] , [88] . Epistemologically, constructivism focuses on how people construct and re-construct knowledge about a specific phenomenon, and has three main assumptions: (1) reality is seen as multiple, at times even incompatible with the phenomenon under consideration; (2) just as primary researchers construct interpretations from participants' data, meta-study researchers also construct understandings about the primary researchers' original findings. Thus, meta-synthesis is a construction of a construction, or a meta-construction; and (3) all constructions are shaped by the historical, social and ideological context in which they originated [54] . The key message here is that reports of any synthesis would benefit from an explicit identification of the underlying philosophical perspectives to facilitate a better understanding of the results, how they were derived, and how they are being interpreted.

4.7. Unit of Analysis

The unit of analysis for each category of review is generally distinct. For the emerging synthesis approaches, the unit of analysis is specific to the intention. In meta-narrative synthesis it is the storyline in diverse research traditions; in rapid review or scoping review, it depends on the focus but could be a concept; and in realist synthesis, it is the theories rather than programs that are the units of analysis. The elements of theory that are important in the analysis are mechanisms of action, the context, and the outcome [107] .

For qualitative synthesis, the units of analysis are generally themes, concepts or theories, although in meta-study, the units of analysis can be research findings (“meta-data-analysis”), research methods (“meta-method”) or philosophical/theoretical perspectives (“meta-theory”) [54] . In quantitative synthesis, the units of analysis range from specific statistics for systematic reviews to effect size of the intervention for meta-analysis. More recently, some systematic reviews focus on theories [115] – [116] , therefore it depends on the research question. Similarly, within conventional literature synthesis the units of analysis also depend on the research purpose, focus and question as well as on the type of research methods incorporated into the review. What is important in all research syntheses, however, is that the unit of analysis needs to be made explicit. Unfortunately, this is not always the case.

4.8. Strengths and Limitations

In this section, we discuss the overarching strengths and limitations of synthesis methodologies as a whole and then highlight strengths and weaknesses across each of our four categories of synthesis.

4.8.1. Strengths of Research Syntheses in General

With the vast proliferation of research reports and the increased ease of retrieval, research synthesis has become more accessible providing a way of looking broadly at the current state of research. The availability of syntheses helps researchers, practitioners, and policy makers keep up with the burgeoning literature in their fields without which evidence-informed policy or practice would be difficult. Syntheses explain variation and difference in the data helping us identify the relevance for our own situations; they identify gaps in the literature leading to new research questions and study designs. They help us to know when to replicate a study and when to avoid excessively duplicating research. Syntheses can inform policy and practice in a way that well-designed single studies cannot; they provide building blocks for theory that helps us to understand and explain our phenomena of interest.

4.8.2. Limitations of Research Syntheses in General

The process of selecting, combining, integrating, and synthesizing across diverse study designs and data types can be complex and potentially rife with bias, even with those methodologies that have clearly defined steps. Just because a rigorous and standardized approach has been used does not mean that implicit judgements will not influence the interpretations and choices made at different stages.

In all types of synthesis, the quantity of data can be considerable, requiring difficult decisions about scope, which may affect relevance. The quantity of available data also has implications for the size of the research team. Few reviews these days can be done independently, in particular because decisions about inclusion and exclusion may require the involvement of more than one person to ensure reliability.

For all types of synthesis, it is likely that in areas with large, amorphous, and diverse bodies of literature, even the most sophisticated search strategies will not turn up all the relevant and important texts. This may be more important in some synthesis methodologies than in others, but the omission of key documents can influence the results of all syntheses. This issue can be addressed, at least in part, by including a library scientist on the research team as required by some funding agencies. Even then, it is possible to miss key texts. In this review, for example, because none of us are trained in or conduct meta-analyses, we were not even aware that we had missed some new developments in this field such as meta-regression [117] – [118] , network meta-analysis [119] – [121] , and the use of individual patient data in meta-analyses [122] – [123] .

One limitation of systematic reviews and meta-analyses is that they rapidly go out of date. We thought this might be true for all types of synthesis, although we wondered if those that produce theory might not be somewhat more enduring. We have not answered this question but it is open for debate. For all types of synthesis, the analytic skills and the time required are considerable so it is clear that training is important before embarking on a review, and some types of review may not be appropriate for students or busy practitioners.

Finally, the quality of reporting in primary studies of all genres is variable so it is sometimes difficult to identify aspects of the study essential for the synthesis, or to determine whether the study meets quality criteria. There may be flaws in the original study, or journal page limitations may necessitate omitting important details. Reporting standards have been developed for some types of reviews (e.g., systematic review, meta-analysis, meta-narrative synthesis, realist synthesis); but there are no agreed upon standards for qualitative reviews. This is an important area for development in advancing the science of research synthesis.

4.8.3. Strengths and Limitations of the Four Synthesis Types

The conventional literature review and now the increasingly common integrative review remain important and accessible approaches for students, practitioners, and experienced researchers who want to summarize literature in an area but do not have the expertise to use one of the more complex methodologies. Carefully executed, such reviews are very useful for synthesizing literature in preparation for research grants and practice projects. They can determine the state of knowledge in an area and identify important gaps in the literature to provide a clear rationale or theoretical framework for a study [14] , [18] . There is a demand, however, for more rigour, with more attention to developing comprehensive search strategies and more systematic approaches to combining, integrating, and synthesizing the findings.

Generally, conventional reviews include diverse study designs and data types that facilitate comprehensiveness, which may be a strength on the one hand, but can also present challenges on the other. The complexity inherent in combining results from studies with diverse methodologies can result in bias and inaccuracies. The absence of clear guidelines about how to synthesize across diverse study types and data [18] has been a challenge for novice reviewers.

Quantitative systematic reviews and meta-analyses have been important in launching the field of evidence-based healthcare. They provide a systematic, orderly and auditable process for conducting a review and drawing conclusions [25] . They are arguably the most powerful approaches to understanding the effectiveness of healthcare interventions, especially when intervention studies on the same topic show very different results. When areas of research are dogged by controversy [25] or when study results go against strongly held beliefs, such approaches can reduce the uncertainty and bring strong evidence to bear on the controversy.

Despite their strengths, they also have limitations. Systematic reviews and meta-analyses do not provide a way of including complex literature comprising various types of evidence including qualitative studies, theoretical work, and epidemiological studies. Only certain types of design are considered and qualitative data are used in a limited way. This exclusion limits what can be learned in a topic area.

Meta-analyses are often not possible because of wide variability in study design, population, and interventions so they may have a narrow range of utility. New developments in meta-analysis, however, can be used to address some of these limitations. Network meta-analysis is used to explore relative efficacy of multiple interventions, even those that have never been compared in more conventional pairwise meta-analyses [121] , allowing for improved clinical decision making [120] . The limitation is that network meta-analysis has only been used in medical/clinical applications [119] and not in public health. It has not yet been widely accepted and many methodological challenges remain [120] – [121] . Meta-regression is another development that combines meta-analytic and linear regression principles to address the fact that heterogeneity of results may compromise a meta-analysis [117] – [118] . The disadvantage is that many clinicians are unfamiliar with it and may incorrectly interpret results [117] .

Some have accused meta-analysis of combining apples and oranges [124] raising questions in the field about their meaningfulness [25] , [28] . More recently, the use of individual rather than aggregate data has been useful in facilitating greater comparability among studies [122] . In fact, Tomas et al. [123] argue that meta-analysis using individual data is now the gold standard although access to the raw data from other studies may be a challenge to obtain.

The usefulness of systematic reviews in synthesizing complex health and social interventions has also been challenged [102] . It is often difficult to synthesize their findings because such studies are “epistemologically diverse and methodologically complex” [ [69] , p.21]. Rigid inclusion/exclusion criteria may allow only experimental or quasi-experimental designs into consideration resulting in lost information that may well be useful to policy makers for tailoring an intervention to the context or understanding its acceptance by recipients.

Qualitative syntheses may be the type of review most fraught with controversy and challenge, while also bringing distinct strengths to the enterprise. Although these methodologies provide a comprehensive and systematic review approach, they do not generally provide definitive statements about intervention effectiveness. They do, however, address important questions about the development of theoretical concepts, patient experiences, acceptability of interventions, and an understanding about why interventions might work.

Most qualitative syntheses aim to produce a theoretically generalizable mid-range theory that explains variation across studies. This makes them more useful than single primary studies, which may not be applicable beyond the immediate setting or population. All provide a contextual richness that enhances relevance and understanding. Another benefit of some types of qualitative synthesis (e.g., grounded formal theory) is that the concept of saturation provides a sound rationale for limiting the number of texts to be included thus making reviews potentially more manageable. This contrasts with the requirements of systematic reviews and meta-analyses that require an exhaustive search.

Qualitative researchers debate about whether the findings of ontologically and epistemological diverse qualitative studies can actually be combined or synthesized [125] because methodological diversity raises many challenges for synthesizing findings. The products of different types of qualitative syntheses range from theory and conceptual frameworks, to themes and rich descriptive narratives. Can one combine the findings from a phenomenological study with the theory produced in a grounded theory study? Many argue yes, but many also argue no.

Emerging synthesis methodologies were developed to address some limitations inherent in other types of synthesis but also have their own issues. Because each type is so unique, it is difficult to identify overarching strengths of the entire category. An important strength, however, is that these newer forms of synthesis provide a systematic and rigorous approach to synthesizing a diverse literature base in a topic area that includes a range of data types such as: both quantitative and qualitative studies, theoretical work, case studies, evaluations, epidemiological studies, trials, and policy documents. More than conventional literature reviews and systematic reviews, these approaches provide explicit guidance on analytic methods for integrating different types of data. The assumption is that all forms of data have something to contribute to knowledge and theory in a topic area. All have a defined but flexible process in recognition that the methods may need to shift as knowledge develops through the process.

Many emerging synthesis types are helpful to policy makers and practitioners because they are usually involved as team members in the process to define the research questions, and interpret and disseminate the findings. In fact, engagement of stakeholders is built into the procedures of the methods. This is true for rapid reviews, meta-narrative syntheses, and realist syntheses. It is less likely to be the case for critical interpretive syntheses.

Another strength of some approaches (realist and meta-narrative syntheses) is that quality and publication standards have been developed to guide researchers, reviewers, and funders in judging the quality of the products [108] , [126] – [127] . Training materials and online communities of practice have also been developed to guide users of realist and meta-narrative review methods [107] , [128] . A unique strength of critical interpretive synthesis is that it takes a critical perspective on the process that may help reconceptualize the data in a way not considered by the primary researchers [72] .

There are also challenges of these new approaches. The methods are new and there may be few published applications by researchers other than the developers of the methods, so new users often struggle with the application. The newness of the approaches means that there may not be mentors available to guide those unfamiliar with the methods. This is changing, however, and the number of applications in the literature is growing with publications by new users helping to develop the science of synthesis [e.g., [129] ]. However, the evolving nature of the approaches and their developmental stage present challenges for novice researchers.

4.9. When to Use Each Approach

Choosing an appropriate approach to synthesis will depend on the question you are asking, the purpose of the review, and the outcome or product you want to achieve. In Additional File 1 , we discuss each of these to provide guidance to readers on making a choice about review type. If researchers want to know whether a particular type of intervention is effective in achieving its intended outcomes, then they might choose a quantitative systemic review with or without meta-analysis, possibly buttressed with qualitative studies to provide depth and explanation of the results. Alternately, if the concern is about whether an intervention is effective with different populations under diverse conditions in varying contexts, then a realist synthesis might be the most appropriate.

If researchers' concern is to develop theory, they might consider qualitative syntheses or some of the emerging syntheses that produce theory (e.g., critical interpretive synthesis, realist review, grounded formal theory, qualitative meta-synthesis). If the aim is to track the development and evolution of concepts, theories or ideas, or to determine how an issue or question is addressed across diverse research traditions, then meta-narrative synthesis would be most appropriate.

When the purpose is to review the literature in advance of undertaking a new project, particularly by graduate students, then perhaps an integrative review would be appropriate. Such efforts contribute towards the expansion of theory, identify gaps in the research, establish the rationale for studying particular phenomena, and provide a framework for interpreting results in ways that might be useful for influencing policy and practice.

For researchers keen to bring new insights, interpretations, and critical re-conceptualizations to a body of research, then qualitative or critical interpretive syntheses will provide an inductive product that may offer new understandings or challenges to the status quo. These can inform future theory development, or provide guidance for policy and practice.

5. Discussion

What is the current state of science regarding research synthesis? Public health, health care, and social science researchers or clinicians have previously used all four categories of research synthesis, and all offer a suitable array of approaches for inquiries. New developments in systematic reviews and meta-analysis are providing ways of addressing methodological challenges [117] – [123] . There has also been significant advancement in emerging synthesis methodologies and they are quickly gaining popularity. Qualitative meta-synthesis is still evolving, particularly given how new it is within the terrain of research synthesis. In the midst of this evolution, outstanding issues persist such as grappling with: the quantity of data, quality appraisal, and integration with knowledge translation. These topics have not been thoroughly addressed and need further debate.

5.1. Quantity of Data

We raise the question of whether it is possible or desirable to find all available studies for a synthesis that has this requirement (e.g., meta-analysis, systematic review, scoping, meta-narrative synthesis [25] , [27] , [63] , [67] , [84] – [85] ). Is the synthesis of all available studies a realistic goal in light of the burgeoning literature? And how can this be sustained in the future, particularly as the emerging methodologies continue to develop and as the internet facilitates endless access? There has been surprisingly little discussion on this topic and the answers will have far-reaching implications for searching, sampling, and team formation.

Researchers and graduate students can no longer rely on their own independent literature search. They will likely need to ask librarians for assistance as they navigate multiple sources of literature and learn new search strategies. Although teams now collaborate with library scientists, syntheses are limited in that researchers must make decisions on the boundaries of the review, in turn influencing the study's significance. The size of a team may also be pragmatically determined to manage the search, extraction, and synthesis of the burgeoning data. There is no single answer to our question about the possibility or necessity of finding all available articles for a review. Multiple strategies that are situation specific are likely to be needed.

5.2. Quality Appraisal

While the issue of quality appraisal has received much attention in the synthesis literature, scholars are far from resolution. There may be no agreement about appraisal criteria in a given tradition. For example, the debate rages over the appropriateness of quality appraisal in qualitative synthesis where there are over 100 different sets of criteria and many do not overlap [49] . These differences may reflect disciplinary and methodological orientations, but diverse quality appraisal criteria may privilege particular types of research [49] . The decision to appraise is often grounded in ontological and epistemological assumptions. Nonetheless, diversity within and between categories of synthesis is likely to continue unless debate on the topic of quality appraisal continues and evolves toward consensus.

5.3. Integration with Knowledge Translation

If research syntheses are to make a difference to practice and ultimately to improve health outcomes, then we need to do a better job of knowledge translation. In the Canadian Institutes of Health Research (CIHR) definition of knowledge translation (KT), research or knowledge synthesis is an integral component [130] . Yet, with few exceptions [131] – [132] , very little of the research synthesis literature even mentions the relationship of synthesis to KT nor does it discuss strategies to facilitate the integration of synthesis findings into policy and practice. The exception is in the emerging synthesis methodologies, some of which (e.g., realist and meta-narrative syntheses, scoping reviews) explicitly involve stakeholders or knowledge users. The argument is that engaging them in this way increases the likelihood that the knowledge generated will be translated into policy and practice. We suggest that a more explicit engagement with knowledge users in all types of synthesis would benefit the uptake of the research findings.

Research synthesis neither makes research more applicable to practice nor ensures implementation. Focus must now turn seriously towards translation of synthesis findings into knowledge products that are useful for health care practitioners in multiple areas of practice and develop appropriate strategies to facilitate their use. The burgeoning field of knowledge translation has, to some extent, taken up this challenge; however, the research-practice gap continues to plague us [133] – [134] . It is a particular problem for qualitative syntheses [131] . Although such syntheses have an important place in evidence-informed practice, little effort has gone into the challenge of translating the findings into useful products to guide practice [131] .

5.4. Limitations

Our study took longer than would normally be expected for an integrative review. Each of us were primarily involved in our own dissertations or teaching/research positions, and so this study was conducted ‘off the sides of our desks.’ A limitation was that we searched the literature over the course of 4 years (from 2008–2012), necessitating multiple search updates. Further, we did not do a comprehensive search of the literature after 2012, thus the more recent synthesis literature was not systematically explored. We did, however, perform limited database searches from 2012–2015 to keep abreast of the latest methodological developments. Although we missed some new approaches to meta-analysis in our search, we did not find any new features of the synthesis methodologies covered in our review that would change the analysis or findings of this article. Lastly, we struggled with the labels used for the broad categories of research synthesis methodology because of our hesitancy to reinforce the divide between quantitative and qualitative approaches. However, it was very difficult to find alternative language that represented the types of data used in these methodologies. Despite our hesitancy in creating such an obvious divide, we were left with the challenge of trying to find a way of characterizing these broad types of syntheses.

6. Conclusion

Our findings offer methodological clarity for those wishing to learn about the broad terrain of research synthesis. We believe that our review makes transparent the issues and considerations in choosing from among the four broad categories of research synthesis. In summary, research synthesis has taken its place as a form of research in its own right. The methodological terrain has deep historical roots reaching back over the past 200 years, yet research synthesis remains relatively new to public health, health care, and social sciences in general. This is rapidly changing. New developments in systematic reviews and meta-analysis, and the emergence of new synthesis methodologies provide a vast array of options to review the literature for diverse purposes. New approaches to research synthesis and new analytic methods within existing approaches provide a much broader range of review alternatives for public health, health care, and social science students and researchers.

Acknowledgments

KSM is an assistant professor in the Faculty of Nursing at the University of Alberta. Her work on this article was largely conducted as a Postdoctoral Fellow, funded by KRESCENT (Kidney Research Scientist Core Education and National Training Program, reference #KRES110011R1) and the Faculty of Nursing at the University of Alberta.

MM's work on this study over the period of 2008-2014 was supported by a Canadian Institutes of Health Research Applied Public Health Research Chair Award (grant #92365).

We thank Rachel Spanier who provided support with reference formatting.

List of Abbreviations (in Additional File 1 )

Conflict of interest: The authors declare that they have no conflicts of interest in this article.

Authors' contributions: KSM co-designed the study, collected data, analyzed the data, drafted/revised the manuscript, and managed the project.

MP contributed to searching the literature, developing the analytic framework, and extracting data for the Additional File.

JB contributed to searching the literature, developing the analytic framework, and extracting data for the Additional File.

WN contributed to searching the literature, developing the analytic framework, and extracting data for the Additional File.

All authors read and approved the final manuscript.

Additional Files: Additional File 1 – Selected Types of Research Synthesis

This Additional File is our dataset created to organize, analyze and critique the literature that we synthesized in our integrative review. Our results were created based on analysis of this Additional File.

Writing in the Health and Social Sciences

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Systematic Literature Reviews: Steps & Resources

Literature review & systematic review steps.

  • What are Literature Reviews?
  • Conducting & Reporting Systematic Reviews
  • Finding Systematic Reviews
  • Tutorials & Tools for Literature Reviews

What are Systematic Reviews? (3 minutes, 24 second YouTube Video)

analysis and synthesis in literature review

These steps for conducting a systematic literature review are listed below . 

Also see subpages for more information about:

  • The different types of literature reviews, including systematic reviews and other evidence synthesis methods
  • Tools & Tutorials
  • Develop a Focused Question
  • Scope the Literature  (Initial Search)
  • Refine & Expand the Search
  • Limit the Results
  • Download Citations
  • Abstract & Analyze
  • Create Flow Diagram
  • Synthesize & Report Results

1. Develop a Focused   Question 

Consider the PICO Format: Population/Problem, Intervention, Comparison, Outcome

Focus on defining the Population or Problem and Intervention (don't narrow by Comparison or Outcome just yet!)

"What are the effects of the Pilates method for patients with low back pain?"

Tools & Additional Resources:

  • PICO Question Help
  • Stillwell, Susan B., DNP, RN, CNE; Fineout-Overholt, Ellen, PhD, RN, FNAP, FAAN; Melnyk, Bernadette Mazurek, PhD, RN, CPNP/PMHNP, FNAP, FAAN; Williamson, Kathleen M., PhD, RN Evidence-Based Practice, Step by Step: Asking the Clinical Question, AJN The American Journal of Nursing : March 2010 - Volume 110 - Issue 3 - p 58-61 doi: 10.1097/01.NAJ.0000368959.11129.79

2. Scope the Literature

A "scoping search" investigates the breadth and/or depth of the initial question or may identify a gap in the literature. 

Eligible studies may be located by searching in:

  • Background sources (books, point-of-care tools)
  • Article databases
  • Trial registries
  • Grey literature
  • Cited references
  • Reference lists

When searching, if possible, translate terms to controlled vocabulary of the database. Use text word searching when necessary.

Use Boolean operators to connect search terms:

  • Combine separate concepts with AND  (resulting in a narrower search)
  • Connecting synonyms with OR  (resulting in an expanded search)

Search:  pilates AND ("low back pain"  OR  backache )

Video Tutorials - Translating PICO Questions into Search Queries

  • Translate Your PICO Into a Search in PubMed (YouTube, Carrie Price, 5:11) 
  • Translate Your PICO Into a Search in CINAHL (YouTube, Carrie Price, 4:56)

3. Refine & Expand Your Search

Expand your search strategy with synonymous search terms harvested from:

  • database thesauri
  • reference lists
  • relevant studies

Example: 

(pilates OR exercise movement techniques) AND ("low back pain" OR backache* OR sciatica OR lumbago OR spondylosis)

As you develop a final, reproducible strategy for each database, save your strategies in a:

  • a personal database account (e.g., MyNCBI for PubMed)
  • Log in with your NYU credentials
  • Open and "Make a Copy" to create your own tracker for your literature search strategies

4. Limit Your Results

Use database filters to limit your results based on your defined inclusion/exclusion criteria.  In addition to relying on the databases' categorical filters, you may also need to manually screen results.  

  • Limit to Article type, e.g.,:  "randomized controlled trial" OR multicenter study
  • Limit by publication years, age groups, language, etc.

NOTE: Many databases allow you to filter to "Full Text Only".  This filter is  not recommended . It excludes articles if their full text is not available in that particular database (CINAHL, PubMed, etc), but if the article is relevant, it is important that you are able to read its title and abstract, regardless of 'full text' status. The full text is likely to be accessible through another source (a different database, or Interlibrary Loan).  

  • Filters in PubMed
  • CINAHL Advanced Searching Tutorial

5. Download Citations

Selected citations and/or entire sets of search results can be downloaded from the database into a citation management tool. If you are conducting a systematic review that will require reporting according to PRISMA standards, a citation manager can help you keep track of the number of articles that came from each database, as well as the number of duplicate records.

In Zotero, you can create a Collection for the combined results set, and sub-collections for the results from each database you search.  You can then use Zotero's 'Duplicate Items" function to find and merge duplicate records.

File structure of a Zotero library, showing a combined pooled set, and sub folders representing results from individual databases.

  • Citation Managers - General Guide

6. Abstract and Analyze

  • Migrate citations to data collection/extraction tool
  • Screen Title/Abstracts for inclusion/exclusion
  • Screen and appraise full text for relevance, methods, 
  • Resolve disagreements by consensus

Covidence is a web-based tool that enables you to work with a team to screen titles/abstracts and full text for inclusion in your review, as well as extract data from the included studies.

Screenshot of the Covidence interface, showing Title and abstract screening phase.

  • Covidence Support
  • Critical Appraisal Tools
  • Data Extraction Tools

7. Create Flow Diagram

The PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) flow diagram is a visual representation of the flow of records through different phases of a systematic review.  It depicts the number of records identified, included and excluded.  It is best used in conjunction with the PRISMA checklist .

Example PRISMA diagram showing number of records identified, duplicates removed, and records excluded.

Example from: Stotz, S. A., McNealy, K., Begay, R. L., DeSanto, K., Manson, S. M., & Moore, K. R. (2021). Multi-level diabetes prevention and treatment interventions for Native people in the USA and Canada: A scoping review. Current Diabetes Reports, 2 (11), 46. https://doi.org/10.1007/s11892-021-01414-3

  • PRISMA Flow Diagram Generator (ShinyApp.io, Haddaway et al. )
  • PRISMA Diagram Templates  (Word and PDF)
  • Make a copy of the file to fill out the template
  • Image can be downloaded as PDF, PNG, JPG, or SVG
  • Covidence generates a PRISMA diagram that is automatically updated as records move through the review phases

8. Synthesize & Report Results

There are a number of reporting guideline available to guide the synthesis and reporting of results in systematic literature reviews.

It is common to organize findings in a matrix, also known as a Table of Evidence (ToE).

Example of a review matrix, using Microsoft Excel, showing the results of a systematic literature review.

  • Reporting Guidelines for Systematic Reviews
  • Download a sample template of a health sciences review matrix  (GoogleSheets)

Steps modified from: 

Cook, D. A., & West, C. P. (2012). Conducting systematic reviews in medical education: a stepwise approach.   Medical Education , 46 (10), 943–952.

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How to write a literature review

Are you writing a literature review as part of a final year project, dissertation, or thesis, or as a standalone piece of work? This page will work through a process of organising and synthesising your sources and then writing a clear and critical final review.

What is a literature review?

A literature review is an account of the current thinking in a specific area of study. Its purpose is to introduce the reader to what has gone before and often to provide you with a foundation that you can build on with your own research. This traditional form of review is sometimes also referred to as a narrative review.

A literature review will often form a section or chapter of a larger piece of research work, such as a dissertation, thesis, or final year project.  It can also be a standalone piece of work.  

A literature review will usually do some or all of the following:

  • Introduce the reader to a specific area of interest.
  • Organise relevant sources thematically, starting with the more general, broader themes and narrowing towards the most specific themes.
  • Introduce key theories relevant to the area of study.
  • Define your understanding of important terms or language used in the research.
  • Include only the most relevant, important or influential sources, carefully selected. It is about quality not quantity!
  • Identify gaps or limitations in existing research.

Considering a body of scholarship as a whole (or in relation to each of your themes) will allow you to 'synthesise' multiple sources and produce an overall summary.

Developing a literature review will help you to develop a level of expertise in your chosen area. By consulting and including a unique combination of sources, you will be able to formulate an informed and original perspective.  Where relevant, this can drive forward your ongoing research.

Writing a Literature Review workshop: book here

A systematic review is a research methodology, often following a standardised and replicable search method and reporting structure that is specific to your discipline. Visit our guidance on systematic reviews for more information.

Organising your sources

As you encounter more and more relevant sources, you will face an ever-expanding amount of reading for yourself. It would take years to read through all of the literature in a specific field from start to finish.

Academic reading, and particularly the process of 'reading around' a topic, is about selective, or targeted reading. Visit our Reading and understanding information Hub to explore approaches to reading for different purposes.

Creating a Literature Matrix can help you to identify the key things that you want to take away from each source. A literature matrix is a simple spreadsheet where you select column titles to suit the aims of your literature review. Are you interested in the research methodology, the scale of the research, the main conclusions, or something else entirely?

Once you have scanned through a source and pulled out the points you are interested in, you can move onto the next source. Organising your reading in this way will also allow you to identify key themes that are emerging in your reading, which you will be able to use later on to plan your review.

You may want to use a reference management tool to help organise and produce your bibliography. Visit the University of Sheffield Library Reference Management pages here .

Make a copy of our Literature matrix template (Google Sheet) and add/delete columns based on the information you want to collect during your search.  Using a spreadsheet means that you can filter and sort your sources, for example, into chronological order, or alphabetically by author.

This downloadable example literature matrix shows how you can lay out your columns.

Synthesising your sources

Once you have a number of sources to work with, you will start to identify key themes emerging. At this point you can start to organise your sources systematically to develop and explore those themes. Can you organise your themes from the broadest to the narrowest and most specific?

A synthesis matrix will help you to identify a thematic structure for your literature review and to understand how the sources that you have found relate to one another. A synthesis matrix is a further spreadsheet that organises your sources by theme and includes a synthesis column, where you can begin to draw out comparisons between the sources. 

Once you have identified a number of sources for each theme in your matrix, you should be able to identify the following:

  • Do the sources build on or develop one another? This may be a chronological process.
  • Do the sources challenge or contradict one another? Do they reveal a debate within the field?
  • Do the sources identify an area of particular interest or a gap in the field?
  • Do the sources help to fill in gaps or complete a bigger picture?

Your synthesis column provides an opportunity for you to comment on multiple sources considered as a whole. It is a space for your critical voice and interpretation, which is a key part of writing a successful literature review.

Make a copy of our synthesis matrix (Google Sheet) to organise your themes and plan how the relevant sources can be synthesised.

Download a completed example synthesis matrix from NC State University (PDF, 34Kb)

Visit our Producing a literature review interactive tutorial - for further guidance.

Writing your review

Once you have done the background reading and organised your sources using a synthesis matrix, the job of writing your review is simply about adding flesh to the bones. You will need to write your review as a narrative account, but you can use your matrix as a framework to help you do so.

A literature review will usually follow a simple structure:

  • Introduction: what is the overall topic area and how have you broken your review down into themes?
  • Theme 1: the broadest, most top-level area (perhaps including some background theory that may have influenced your thinking).
  • Theme 2, theme 3, theme 4, etc. Your themes should get progressively more specific and closer to the focus of your research.
  • Conclusion: how has this informed your thinking and (if the review is part of a bigger project) what are your research aims and objectives? 

Your review may be broken down by section headings or be a continuous flow with themes clearly separated in a paragraph structure. Each section or paragraph will describe that theme and finish by summarising your overview of a theme (the synthesis part of the matrix above, which includes your critical analysis). 

Our web page How to structure a paragrap h has further guidance to ensure your paragraphs are clear and contain your synthesis and critical analysis.

For advice and feedback on your own review, including referencing, synthesis and academic arguments, please book a writing advisory service appointment.

Make an appointment (student login required)

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Online Guide to Writing and Research

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  • Online Guide to Writing

Critical Strategies and Writing

One of the basic academic writing activities is researching your topic and what others have said about it. Your goal should be to draw thoughts, observations, and claims about your topic from your research. We call this process of drawing from multiple sources “ synthesis .” Click on the accordion items below for more information.

Definition, Use, and Sample Synthesis

Synthesis defined.

Synthesis Emerges from Analysis

Synthesis emerges from analytical activities we discussed on the previous page: comparative analysis and analysis for cause and effect . For example, to communicate where scholars agree and where they disagree, one must analyze their work for similarities and differences. Also crucial for understanding scholarly discourse is understanding how a particular work of scholarship shapes the scholarship of others, causing them to head in new directions.

When Should Synthesis Be Used?

When to Use Synthesis

Many college assignments require synthesis. A literature review, for example, requires that you make explanatory claims regarding a body of research. These should go beyond summary (mere description) to provide helpful characterizations that aid in understanding. Literature reviews can stand on their own, but often they are a part of a research paper, and research papers are where you will probably use synthesis most often.

The purpose of a research paper is to derive meaning from a body of information collected through research. It is your job, as the writer, to communicate that meaning to your readers. Doing this requires that you develop an informed and educated opinion of what your research suggests about your subject. Communicating this opinion requires synthesis.

Sample Synthesis

In 1655, an embassy of Dutch Jews led by Rabbi Menassah ben Israel traveled to London to meet with the Commonwealth’s new Lord Protector, Oliver Cromwell. The informal “Readmission” of Jews—who had been expelled from England by royal edict in 1290—resulting from the Whitehall conference was once hailed as a high point in the history of toleration. Yet in recent years, scholars have increasingly challenged the progressive nature of this event, both in its substance and its motivation (Kaplan 2007; Katznelson 2010; Walsham 2006) . “Toleration” in this case, as in many others, did not entail religious freedom or civic equality; Jews in England were granted legal residency and permitted to worship privately, but citizenship, public worship, and the printing of anything that “opposeth the Christian religion” remained off the cards. As for its motivation, Edward Whalley’s twofold argument was representative: the Jews “will bring in much wealth into this Commonwealth: and where wee both pray for theyre conversion and beleeve it shal be, I knowe not why wee shold deny the means” (Marshall 2006, 381–82) 

(Bejan, 2015, p. 1103).

The author of the above passage, Teresa Bejan, has synthesized the work of a number of other scholars (Kaplan, Katznelson, Walsham, and Marshall) to situate her argument.  Note how not all of these scholars are directly quoted, but they are cited because their work forms the basis of Bejan's work.

Key Takeaways

  • Synthesizing allows you to carry an argument or stance you adopt within a paper in your own words, based on conclusions you have come to about the topic.
  • Synthesizing contributes to confidence about your stance and topic.

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Table of Contents: Online Guide to Writing

Chapter 1: College Writing

How Does College Writing Differ from Workplace Writing?

What Is College Writing?

Why So Much Emphasis on Writing?

Chapter 2: The Writing Process

Doing Exploratory Research

Getting from Notes to Your Draft

Introduction

Prewriting - Techniques to Get Started - Mining Your Intuition

Prewriting: Targeting Your Audience

Prewriting: Techniques to Get Started

Prewriting: Understanding Your Assignment

Rewriting: Being Your Own Critic

Rewriting: Creating a Revision Strategy

Rewriting: Getting Feedback

Rewriting: The Final Draft

Techniques to Get Started - Outlining

Techniques to Get Started - Using Systematic Techniques

Thesis Statement and Controlling Idea

Writing: Getting from Notes to Your Draft - Freewriting

Writing: Getting from Notes to Your Draft - Summarizing Your Ideas

Writing: Outlining What You Will Write

Chapter 3: Thinking Strategies

A Word About Style, Voice, and Tone

A Word About Style, Voice, and Tone: Style Through Vocabulary and Diction

Critical Strategies and Writing: Analysis

Critical Strategies and Writing: Evaluation

Critical Strategies and Writing: Persuasion

Critical Strategies and Writing: Synthesis

Developing a Paper Using Strategies

Kinds of Assignments You Will Write

Patterns for Presenting Information

Patterns for Presenting Information: Critiques

Patterns for Presenting Information: Discussing Raw Data

Patterns for Presenting Information: General-to-Specific Pattern

Patterns for Presenting Information: Problem-Cause-Solution Pattern

Patterns for Presenting Information: Specific-to-General Pattern

Patterns for Presenting Information: Summaries and Abstracts

Supporting with Research and Examples

Writing Essay Examinations

Writing Essay Examinations: Make Your Answer Relevant and Complete

Writing Essay Examinations: Organize Thinking Before Writing

Writing Essay Examinations: Read and Understand the Question

Chapter 4: The Research Process

Planning and Writing a Research Paper

Planning and Writing a Research Paper: Ask a Research Question

Planning and Writing a Research Paper: Cite Sources

Planning and Writing a Research Paper: Collect Evidence

Planning and Writing a Research Paper: Decide Your Point of View, or Role, for Your Research

Planning and Writing a Research Paper: Draw Conclusions

Planning and Writing a Research Paper: Find a Topic and Get an Overview

Planning and Writing a Research Paper: Manage Your Resources

Planning and Writing a Research Paper: Outline

Planning and Writing a Research Paper: Survey the Literature

Planning and Writing a Research Paper: Work Your Sources into Your Research Writing

Research Resources: Where Are Research Resources Found? - Human Resources

Research Resources: What Are Research Resources?

Research Resources: Where Are Research Resources Found?

Research Resources: Where Are Research Resources Found? - Electronic Resources

Research Resources: Where Are Research Resources Found? - Print Resources

Structuring the Research Paper: Formal Research Structure

Structuring the Research Paper: Informal Research Structure

The Nature of Research

The Research Assignment: How Should Research Sources Be Evaluated?

The Research Assignment: When Is Research Needed?

The Research Assignment: Why Perform Research?

Chapter 5: Academic Integrity

Academic Integrity

Giving Credit to Sources

Giving Credit to Sources: Copyright Laws

Giving Credit to Sources: Documentation

Giving Credit to Sources: Style Guides

Integrating Sources

Practicing Academic Integrity

Practicing Academic Integrity: Keeping Accurate Records

Practicing Academic Integrity: Managing Source Material

Practicing Academic Integrity: Managing Source Material - Paraphrasing Your Source

Practicing Academic Integrity: Managing Source Material - Quoting Your Source

Practicing Academic Integrity: Managing Source Material - Summarizing Your Sources

Types of Documentation

Types of Documentation: Bibliographies and Source Lists

Types of Documentation: Citing World Wide Web Sources

Types of Documentation: In-Text or Parenthetical Citations

Types of Documentation: In-Text or Parenthetical Citations - APA Style

Types of Documentation: In-Text or Parenthetical Citations - CSE/CBE Style

Types of Documentation: In-Text or Parenthetical Citations - Chicago Style

Types of Documentation: In-Text or Parenthetical Citations - MLA Style

Types of Documentation: Note Citations

Chapter 6: Using Library Resources

Finding Library Resources

Chapter 7: Assessing Your Writing

How Is Writing Graded?

How Is Writing Graded?: A General Assessment Tool

The Draft Stage

The Draft Stage: The First Draft

The Draft Stage: The Revision Process and the Final Draft

The Draft Stage: Using Feedback

The Research Stage

Using Assessment to Improve Your Writing

Chapter 8: Other Frequently Assigned Papers

Reviews and Reaction Papers: Article and Book Reviews

Reviews and Reaction Papers: Reaction Papers

Writing Arguments

Writing Arguments: Adapting the Argument Structure

Writing Arguments: Purposes of Argument

Writing Arguments: References to Consult for Writing Arguments

Writing Arguments: Steps to Writing an Argument - Anticipate Active Opposition

Writing Arguments: Steps to Writing an Argument - Determine Your Organization

Writing Arguments: Steps to Writing an Argument - Develop Your Argument

Writing Arguments: Steps to Writing an Argument - Introduce Your Argument

Writing Arguments: Steps to Writing an Argument - State Your Thesis or Proposition

Writing Arguments: Steps to Writing an Argument - Write Your Conclusion

Writing Arguments: Types of Argument

Appendix A: Books to Help Improve Your Writing

Dictionaries

General Style Manuals

Researching on the Internet

Special Style Manuals

Writing Handbooks

Appendix B: Collaborative Writing and Peer Reviewing

Collaborative Writing: Assignments to Accompany the Group Project

Collaborative Writing: Informal Progress Report

Collaborative Writing: Issues to Resolve

Collaborative Writing: Methodology

Collaborative Writing: Peer Evaluation

Collaborative Writing: Tasks of Collaborative Writing Group Members

Collaborative Writing: Writing Plan

General Introduction

Peer Reviewing

Appendix C: Developing an Improvement Plan

Working with Your Instructor’s Comments and Grades

Appendix D: Writing Plan and Project Schedule

Devising a Writing Project Plan and Schedule

Reviewing Your Plan with Others

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  • Volume 14, Issue 9
  • Guideline concordant screening and monitoring of extrapyramidal symptoms in patients prescribed antipsychotic medication: a protocol for a systematic literature review and narrative synthesis
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  • http://orcid.org/0009-0008-8045-1704 Rebekah Aubry 1 ,
  • http://orcid.org/0000-0002-7777-0981 Thomas Hastings 2 , 3 ,
  • http://orcid.org/0009-0001-5954-4702 Micheal Morgan 4 ,
  • Jacqueline Hastings 5 ,
  • Marie Bolton 6 ,
  • Maura Grummell 7 ,
  • Sinead Killeen 1 ,
  • Cathal Coyne 8 ,
  • Risa Shorr 9 ,
  • http://orcid.org/0000-0003-4877-7233 Marco Solmi 10
  • 1 Department of Psychiatry , Lucena Clinic Services , Dublin , Ireland
  • 2 Department of Psychiatry , McMaster University , Hamilton , Ontario , Canada
  • 3 Department of Psychiatry , University of Toronto , Toronto , Ontario , Canada
  • 4 Department of Psychiatry , South Louth CAMHS , Drogheda , Ireland
  • 5 School of Medicine , UCD , Dublin , Ireland
  • 6 Department of Child and Adolescent Psychiatry , St Vincent's Hospital Fairview , Dublin , Ireland
  • 7 Department of Psychiatry , Mater Misericordiae University Hospital , Dublin , Ireland
  • 8 Department of Child and Adolescent Psychiatry , West Kildare CAMHS Linn Dara , Abbeylands Clane , Ireland
  • 9 Learning Services , Ottawa Hospital , Ottawa , Ontario , Canada
  • 10 Ottawa Hospital Research Institute , Ottawa , Ontario , Canada
  • Correspondence to Dr Rebekah Aubry; rebekah.aubry{at}sjog.ie

Introduction Given the increasing rates of antipsychotic use in multiple psychiatric conditions, greater attention to the assessment, monitoring and documentation of their side effects is warranted. While a significant degree of attention has been provided to metabolic side effect monitoring, comparatively little is known about how clinicians screen for, document and monitor the motor side effects of antipsychotics (ie, parkinsonism, akathisia, dystonia and dyskinesias, collectively ‘extrapyramidal side effects’, EPS). This review aims to systematically assess the literature for insights into current trends in EPS monitoring practices within various mental health settings globally.

Methods and analysis An electronic search will be performed using the OVID Medline, PubMed, Embase, CINAHL and APA PsycINFO databases for studies published in the last quarter century (1998 to present day). Two independent reviewers will conduct the initial title and abstract screenings, using predetermined criteria for inclusion and exclusion. A third reviewer will resolve disagreements if consensus cannot be reached. If selected for inclusion, full-text data extraction will then be conducted using a pilot-tested data extraction form. Quality assessment will be conducted for all included studies using a modified version of the Quality Improvement Minimum Quality Criteria Set. A narrative synthesis and summary of the data will be provided. All stages of the review process will be reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

Ethics and dissemination Ethical approval is not required. Findings will be peer reviewed, published and shared verbally, electronically and in print with interested clinicians and will also be presented as posters or talks at relevant medical conferences and meetings.

PROSPERO registration number CRD42023482372.

  • Systematic Review
  • Schizophrenia & psychotic disorders
  • Protocols & guidelines

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See:  http://creativecommons.org/licenses/by-nc/4.0/ .

https://doi.org/10.1136/bmjopen-2024-087632

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STRENGTHS AND LIMITATIONS OF THIS STUDY

The search strategy was developed a priori in collaboration with an experienced health sciences librarian and involves a comprehensive search across five large databases and platforms.

The protocol follows the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols guidelines enhancing replicability and transparency.

Included studies will be rated based on their methodological quality using a modified version of the Quality Improvement Minimum Quality Criteria Set quality assessment tool developed by Hempel et al , which is suitable for the quality assessment of various types of service evaluation studies.

Due to resource constraints, the literature search will be restricted to English-only, peer-reviewed publications, possibly increasing the risk of selection bias and limiting the generalisability of review findings.

Introduction

Second generation antipsychotics (SGAs) are broadly used in clinical practice, not only for the treatment of psychotic and bipolar disorders but also for a variety of other conditions. 1–3 While SGAs are associated with a lower risk of motor side effects (ie, parkinsonism, akathisia, dystonia and dyskinesias, collectively ‘extrapyramidal side effects’, EPSs) than first-generation antipsychotics the rates of EPS remain significant. 4–8 Furthermore, EPSs are associated with impaired quality of life, medication non-adherence, increased morbidity, mortality, caregiver burden, utilisation of healthcare resources and higher medical costs. 8–16 This has resulted in some advocating for ‘better monitoring … to assess their true effect on patients’ quality of life and functioning and to prevent underascertainment’, 17 something especially important in higher risk populations, for instance, children, adolescents and the elderly. 18–20 The most recent American Psychiatric Association’s guidelines (2020) for the treatment of patients with schizophrenia calls for clinical assessment of EPS at baseline or initial assessment, at each subsequent visit as well as an assessment using a ‘structured instrument’ every 6 months in patients at increased risk of tardive dyskinesia and every 12 months for all other patients. 21 In the UK, the National Institute for Health and Care Excellence guidelines recommend assessment of any movement disorders before starting antipsychotic medication as part of baseline investigations and to monitor and record side effects of treatment and their impact on functioning, and the emergence of movement disorders, regularly and systematically throughout treatment and especially during titration. 22 Unfortunately, evidence demonstrates that actual monitoring rates fall far below these standards. 23–25

Rationale for the review

While a significant degree of attention has been provided to metabolic side effect monitoring, with several systematic reviews conducted on the subject, 26 27 comparatively little is known about EPS monitoring practices.

When it comes to EPS, its incidence and prevalence in research and naturalistic settings have been thoroughly investigated in numerous studies and reviews. 4–6 28 However, there seems to be a paucity of data about current practices relating to how clinicians screen for, monitor and document EPS in patients prescribed antipsychotics. Gaining a better understanding of current practice may allow for the introduction of effective interventions that help address the existing discrepancy between current practice and best practice.

Aim and objectives

The aim of this review is to systematically assess the literature, seeking insights into current EPS monitoring practices within various mental health settings globally.

Our three main objectives are as follows: (1) to identify the extent to which patients prescribed antipsychotic medication receive guideline concordant monitoring, (2) to gather data on interventions that have been proposed to improve this aspect of care and (3) to identify any existing barriers.

Research questions

In accordance with the aim and objectives outlined above, this review will seek to answer the following questions as regards EPS monitoring for patients who are prescribed antipsychotic medication:

Which guidelines if any are being used to guide current practice and arerecommended standards being met? What screening tools are being used?

What is the frequency of monitoring? Has it improved or worsened over the years?

What interventions have been proposed to improve monitoring standards?

What are some of the possible barriers to adequate monitoring?

Methods and design

All stages of the review process including literature searching, screening, applying inclusion and exclusion criteria and data extraction will be reported and documented in accordance with the Preferred Reporting Items for Systematic Review and Met-Analysis Protocol (PRISMA-P) statement. 29 The PRISMA-P was used to guide the development of the review protocol (see online supplemental file 1 for PRISMA-P checklist). 30 In accordance with the guidelines, this systematic review protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) under the reference number CRD42023482372. Any amendments to the protocol will be reported when publishing the results.

Supplemental material

Inclusion and exclusion criteria (eligibility of studies).

These are grouped under the following seven subsections:

Study design

Study designs aimed at gathering data on current practices relating to EPS documentation and monitoring as well as studies describing interventions developed to improve clinical performance in the area of documentation and monitoring of EPS will be included in the review. Examples of study designs that will be included are as follows:

Clinical audits without intervention.

Clinical audits with completed audit cycles after intervention.

Service evaluations without a quality improvement intervention.

Service evaluations following a quality improvement intervention.

However, the following study design types will be excluded:

Case reports.

Any trial design, including randomized controlled trials(RCTs).

Literature reviews.

Discussion and viewpoint studies.

Grey literature.

Abstract-only publications.

Epidemiological studies of incidence/prevalence of EPS.

Survey designs.

Types of intervention

All types of interventions concerned with the assessment, screening and monitoring of EPS will be included. This will involve gathering data on the types of processes currently used to carry out EPS monitoring and documentation as well as on any proposed interventions aimed at improving EPS documentation and monitoring such as educational interventions, adoption of novel screening instruments, etc.

Study language

This systematic review will be restricted to English language studies only.

Publication dates

Studies published from 1998 to the present will be included, spanning the last 25 years of clinical practice. We consider this sufficiently representative of contemporary trends in practice.

Study population/demographics

The first population of interest includes patients of all ages and genders receiving treatment for one or more mental health conditions and prescribed one or more antipsychotic medications. While it is true that EPS can manifest spontaneously in patients who were never exposed to antipsychotic agents 31 32 or can be caused by substances other than antipsychotics, 33–35 a substantial proportion of reported EPS is attributed to antipsychotic medication. 6 36 37 Moreover, even within cohorts of previously neuroleptic naïve patients, research suggests that dopamine D2 receptor antagonist antipsychotics interact with the disease process in such a way that ‘precipitates’ and ‘accentuates’ movement disorders intrinsic to schizophrenia’. 38 This review will, therefore, focus on patients prescribed antipsychotic medication, as they may be at higher risk of developing severe EPS. In addition, most available guidelines on EPS monitoring specifically refer to patients prescribed antipsychotic medications.

The second population of interest includes the healthcare professionals involved in the care of the patients (eg, nurses, residents, clinicians and pharmacists) and tasked with carrying out EPS monitoring.

Study settings

Studies reporting on EPS monitoring practices in any naturalistic, real-world clinical setting, including inpatient hospitals, day hospitals, outpatient clinics, community settings, etc will be included.

Other phenomena of interest

Where available, data on the views, experiences and behaviours of healthcare professionals and patients involved in the assessment, screening and monitoring of EPS will also be collected.

Patient and public involvement

Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this protocol.

Information sources

Electronic sources.

The literature search was conducted using the following five databases and search platforms: OVID Medline, PubMed, EMBASE, PsycINFO and CINAHL. The initial search covers 25 years and includes studies published between April 1998 and April 2023. These searches will be re-run immediately prior to the final analysis (projected to take place in September 2024) and potential further studies will be retrieved for inclusion, ensuring that the most up-to-date information is presented in the review. The reference lists of all eligible articles will be manually searched to identify any additional relevant citations to ensure a comprehensive search.

Search strategy

Review authors RA and RS (librarian and information specialist with expertise in electronic searching) developed and ran a comprehensive search strategy. A scoping search was undertaken against each database to inform how the search terms were being translated and hence to identify the corresponding text words in each database. Following this, the complete search strategy was tested for its sensitivity to locate the key papers that the researchers are already aware of, along with relevant articles which are consistent with the inclusion criteria just before running the search through all the selected search engines.

The search strategy used variations in text words found in the title, abstract or keyword fields, and relevant focused subject headings to retrieve articles combining the following three search concepts, linked by the Boolean operator ‘AND’:

(1) One or more medication terms: antipsychotic* OR psychotropic* OR haloperidol OR olanzapine OR quetiapine OR risperidone OR cariprazine OR amisulpride OR aripiprazole OR lurasidone etc… (to include full list of antipsychotic medication listed as per the WHO Collaboration Centre for Drug Statistics Methodology ATC classification).

(2) One or more EPS terms: “Extrapyramidal symptom*” OR “Extrapyramidal side effect*” OR “drug-induced movement disorder*” OR ‘Drug-Related Side Effects and Adverse Reactions’ OR ‘movement side effects’ OR Dystonia OR ‘acute dystonia’ OR parkinsonism OR ‘drug-induced parkinsonism’ OR akathisia OR “tardive dyskinesia” OR tremor

(3) One or more terms relating to monitoring, screening, documenting or auditing clinical practice (including screening instruments): ‘Monitoring’ OR ‘Screening’ OR ‘Documenting’ OR ‘Documentation’ OR ‘Assessing’ OR ‘Assessment’ OR ‘Abnormal Involuntary Movement Scale’ OR ‘Extrapyramidal Symptom Rating Scale’ OR ‘Simpson-Angus Scale’ OR ‘Barnes Akathisia Scale’.

The search included all relevant synonyms, truncations and Mesh terms. Full details of search terms used for the OVID Medline search are shown in online supplemental file 2 . A similar search was conducted using the other databases and search platforms. The full search strategy is available on request from the corresponding author.

Study records

Data management.

The search results will be uploaded into web-based, systematic review management software (Covidence). Duplicates will be removed automatically by Covidence software. Authors RA and MM will scan through the results to remove any remaining duplicate records manually. Using Covidence, the initial title and abstract screening, and the full-text review will be logged. All standardised forms will be piloted and revised as needed by the reviewers before starting the review.

Screening and selection process

After identification of articles from searching the electronic databases, titles and abstracts will be screened independently by two review authors according to the predefined eligibility criteria. Disagreements will be resolved by consensus and the opinion of a third reviewer will be sought if necessary. The full-text copies of each potentially relevant study will then be retrieved and screened independently by at least two reviewers including the first author (RA). Consensus will be reached through discussion, and in the event that no consensus can be reached for a study, a third reviewer will arbitrate. All studies not meeting the eligibility criteria will be excluded. The results will be reported using the PRISMA flow diagram.

Data extraction and reporting of results

A standardised data extraction form will be developed to extract all relevant data from included studies. Information to be extracted will be as follows:

Study characteristics: authors, date, settings, country of origin, study design and sample size.

Patient characteristics: demographic data (age, gender, diagnosis, type of antipsychotic prescribed, etc.).

Monitoring characteristics: frequency, use of a structured tool, healthcare professionals involved in monitoring, guidelines followed, etc.

Intervention characteristics: (if study incorporated a preintervention/postintervention design): educational intervention, adoption of a new instrument, etc.

The data extraction form will be piloted on a small random sample (n=3) of the illegible studies to assess its reliability in extracting the targeted study data. Review authors TH, MB and SK will each independently conduct data extraction on the three studies. Review authors RA and MM will then review this extracted data, checking against the full text of the three studies for any discrepancies (eg, errors, omissions or failure to have consensus in any area) and will decide on how to resolve any that may arise. If the above pilot data extraction process is deemed reliable then the review authors TH, MB and SK will each independently conduct data extraction on the remaining studies in the systematic review. Review authors RA and MM will then cross-check the extracted data against the full-text articles in a similar process to that highlighted above.

Additionally, study authors will be contacted if necessary to gain information for clarification purposes and access to raw material when needed.

Critical appraisal of study quality

Authors RA and MM will use the Quality Improvement Minimum Quality Criteria Set (QI-MQCS) developed by Hempel et al to conduct the quality assessment of included studies. 39 Disagreements will be resolved by consensus; the opinion of a third reviewer (MG) will be sought if necessary. The QI-MQCS is a 16-domain, validated, reliable critical appraisal tool that assesses expert-endorsed QI domains for studies that include a QI intervention component. The QI-MQCS will be modified to be suitable for the body of studies included in our review, and in particular, to be able to assess studies with no intervention component, that is, clinical audits and service evaluations with no intervention. This will involve accepting a broader definition of several domains of the appraisal instrument to include studies evaluating existing services or standards in addition to QI intervention. This approach was chosen in the absence of a suitable tool for critical appraisal of service evaluation studies with no intervention component.

The QI-MQCS tool is designed to provide a score for each domain as well as a total score, which is expressed as a percentage of the maximum possible score.

Data synthesis

In this review, the search is expected to reveal heterogeneous studies and meta-analysis of study findings is therefore not a study objective. Therefore, data synthesis will take the form of a structured narrative synthesis of the included studies. The defining characteristic of a narrative synthesis is that it adopts a textual approach to the process of synthesis in order to provide answers to the identified research questions in a structured manner. Study findings pertaining to the following three themes will be examined and synthesised: (1) Data concerning the extent and quality of EPS monitoring being carried out in various mental health settings will be summarised. (2) Following this, details about any potential interventions employed to improve monitoring practices will be synthesised. And finally, (3) Information about any identifiable barriers or facilitators to guideline concordant EPS monitoring will be synthesised and discussed.

Study status

The study is ongoing and is expected to be completed by September 2024.

Proposed value of the systematic review and use of the findings

This systematic review seeks to shed light on the existing patterns of EPS monitoring occurring within various mental health settings. The findings of this systematic review may be of interest to mental health organisations and services as they are expected to provide insights into the potential barriers or facilitators (including possible quality improvement interventions) influencing whether EPS monitoring is carried out in a guideline concordant manner. This may in turn encourage organisations and services to assess their existing EPS monitoring practice and/or lead them to consider the adoption or development of interventions to improve monitoring standards.

Ethics statements

Patient consent for publication.

Not applicable.

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Contributors RA is the author acting as guarantor. The study was conceived by RA, MS, MM and TH. RA and MM developed the eligibility criteria, search strategy, quality assessment strategy and data extraction plan with guidance from MS and RS. RA, TH and MM wrote the manuscript. MS, MB, MM, MG, JH, SK and CC read all drafts of the manuscript, provided feedback and approved the final manuscript. All contributors meet the ICMJE criteria for authorship.

Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

Competing interests MS has received honoraria/has been a consultant for AbbVie, Angelini, Lundbeck, Otsuka.

Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

Provenance and peer review Not commissioned; externally peer reviewed.

Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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A comprehensive review on microbial diversity and anticancer compounds derived from seaweed endophytes: a pharmacokinetic and pharmacodynamic approach

  • Published: 14 September 2024
  • Volume 206 , article number  403 , ( 2024 )

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analysis and synthesis in literature review

  • P. V. Tharani 1 &
  • K. V. Bhaskara Rao   ORCID: orcid.org/0000-0002-6327-1452 1  

Seaweed endophytes are a rich source of microbial diversity and bioactive compounds. This review provides a comprehensive analysis of the microbial diversity associated with seaweeds and their interaction between them. These diverse bacteria and fungi have distinct metabolic pathways, which result in the synthesis of bioactive compounds with potential applications in a variety of health fields. We examine many types of seaweed-associated microorganisms, their bioactive metabolites, and their potential role in cancer treatment using a comprehensive literature review. By incorporating recent findings, we hope to highlight the importance of seaweed endophytes as a prospective source of novel anticancer drugs and promote additional studies in this area. We also investigate the pharmacokinetic and pharmacodynamic profiles of these bioactive compounds because understanding their absorption, distribution, metabolism, excretion (ADMET), and toxicity profiles is critical for developing bioactive compounds with anticancer potential into effective cancer drugs. This knowledge ensures the safety and efficacy of proposed medications prior to clinical trials. This study not only provides promise for novel and more effective treatments for cancer with fewer side effects, but it also emphasizes the necessity of sustainable harvesting procedures and ethical considerations for protecting the delicate marine ecology during bioprospecting activities.

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The authors are thankful to Vellore Institute of Technology, Vellore for providing research facilities in School of Bio-Sciences and Technology.

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Tharani, P.V., Rao, K.V.B. A comprehensive review on microbial diversity and anticancer compounds derived from seaweed endophytes: a pharmacokinetic and pharmacodynamic approach. Arch Microbiol 206 , 403 (2024). https://doi.org/10.1007/s00203-024-04121-1

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    How to synthesize. In the synthesis step of a literature review, researchers analyze and integrate information from selected sources to identify patterns and themes. This involves critically evaluating findings, recognizing commonalities, and constructing a cohesive narrative that contributes to the understanding of the research topic. Synthesis.

  10. LibGuides: Literature Review How To: Synthesizing Sources

    Synthesis writing is a form of analysis related to comparison and contrast, classification and division. On a basic level, synthesis requires the writer to pull together two or more summaries, looking for themes in each text. ... In a literature review you will be combining material from several texts to create a new text - your literature ...

  11. Step 2: Analysis, synthesis, critique

    Skill #1: Analysis. Analysis means that you have carefully read a wide range of the literature on your topic and have understood the main themes, and identified how the literature relates to your own topic. Carefully read and analyze the articles you find in your search, and take notes. Notice the main point of the article, the methodologies ...

  12. Literature Reviews: Synthesis

    Synthesis is an important element of academic writing, demonstrating comprehension, analysis, evaluation and original creation. With synthesis you extract content from different sources to create an original text. While paraphrase and summary maintain the structure of the given source (s), with synthesis you create a new structure.

  13. What is a Literature Review? How to Write It (with Examples)

    A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship ...

  14. Literature Synthesis: Guide To Synthesise & Write Literature Review

    Published on: June 19, 2024. Literature synthesis is a crucial skill for researchers and scholars, allowing them to integrate findings from multiple sources into a coherent analysis. Mastering literature synthesis will enhance your research and writing skills. This guide will walk you through the process of synthesising and writing a literature ...

  15. Using a Synthesis Matrix

    3. Search the literature. Super Searching ; Finding the Full Text ; Citation Searching This link opens in a new window; When to stop searching ; 4. Manage your references. Citation Management ; Annotating Articles Tip ; 5. Critically analyze and evaluate; 6. Synthesize. How to Review the Literature ; Using a Synthesis Matrix ; 7. Write ...

  16. How To Write Synthesis In Research: Example Steps

    Step 1 Organize your sources. Step 2 Outline your structure. Step 3 Write paragraphs with topic sentences. Step 4 Revise, edit and proofread. When you write a literature review or essay, you have to go beyond just summarizing the articles you've read - you need to synthesize the literature to show how it all fits together (and how your own ...

  17. Chapter 7: Synthesizing Sources

    A literature review is not an annotated bibliography, organized by title, author, or date of publication. Rather, it is grouped by topic to create a whole view of the literature relevant to your research question. Figure 7.1. Your synthesis must demonstrate a critical analysis of the papers you collected as well as your ability to integrate the ...

  18. Research Guides: Writing the Literature Review: Step 5: Synthesize

    Synthesis refers to combining separate elements to create a whole. When reading through your sources (peer reviewed journal articles, books, research studies, white papers etc.) you will pay attention to relationships between the studies, between groups in the studies, and look for any pattterns, similarities or differences.

  19. What Synthesis Methodology Should I Use? A Review and Analysis of

    Similarly, within conventional literature synthesis the units of analysis also depend on the research purpose, focus and question as well as on the type of research methods incorporated into the review. What is important in all research syntheses, however, is that the unit of analysis needs to be made explicit.

  20. Analysis and Synthesis

    5.2.1 Creating a Data Matrix. Data analysis of a body or sample of literature often requires the reviewer to first deconstruct each literature source into its most basic elements (Torraco 2005).One of the essential first steps in the data analysis stage is the creation of a review matrix (Garrard 2017).The review matrix provides a structured document to use during analysis and supports the ...

  21. Literature Reviews and Synthesis Tools

    2. Scope the Literature. A "scoping search" investigates the breadth and/or depth of the initial question or may identify a gap in the literature. Eligible studies may be located by searching in: Background sources (books, point-of-care tools) Article databases; Trial registries; Grey literature; Cited references; Reference lists

  22. How to write a literature review

    A synthesis matrix will help you to identify a thematic structure for your literature review and to understand how the sources that you have found relate to one another. A synthesis matrix is a further spreadsheet that organises your sources by theme and includes a synthesis column, where you can begin to draw out comparisons between the sources.

  23. State-of-the-art literature review methodology: A six-step approach for

    Introduction Researchers and practitioners rely on literature reviews to synthesize large bodies of knowledge. Many types of literature reviews have been developed, each targeting a specific purpose. However, these syntheses are hampered if the review type's paradigmatic roots, methods, and markers of rigor are only vaguely understood. One literature review type whose methodology has yet to ...

  24. Critical Strategies and Writing: Synthesis

    Synthesis Emerges from Analysis. ... Many college assignments require synthesis. A literature review, for example, requires that you make explanatory claims regarding a body of research. These should go beyond summary (mere description) to provide helpful characterizations that aid in understanding. Literature reviews can stand on their own ...

  25. Guideline concordant screening and monitoring of extrapyramidal

    All stages of the review process including literature searching, screening, applying inclusion and exclusion criteria and data extraction will be reported and documented in accordance with the Preferred Reporting Items for Systematic Review and Met-Analysis Protocol (PRISMA-P) statement.29 The PRISMA-P was used to guide the development of the ...

  26. A comprehensive review on microbial diversity and anticancer compounds

    Seaweed endophytes are a rich source of microbial diversity and bioactive compounds. This review provides a comprehensive analysis of the microbial diversity associated with seaweeds and their interaction between them. These diverse bacteria and fungi have distinct metabolic pathways, which result in the synthesis of bioactive compounds with potential applications in a variety of health fields ...