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Systematic Literature Review or Literature Review?

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As a researcher, you may be required to conduct a literature review. But what kind of review do you need to complete? Is it a systematic literature review or a standard literature review? In this article, we’ll outline the purpose of a systematic literature review, the difference between literature review and systematic review, and other important aspects of systematic literature reviews.

What is a Systematic Literature Review?

The purpose of systematic literature reviews is simple. Essentially, it is to provide a high-level of a particular research question. This question, in and of itself, is highly focused to match the review of the literature related to the topic at hand. For example, a focused question related to medical or clinical outcomes.

The components of a systematic literature review are quite different from the standard literature review research theses that most of us are used to (more on this below). And because of the specificity of the research question, typically a systematic literature review involves more than one primary author. There’s more work related to a systematic literature review, so it makes sense to divide the work among two or three (or even more) researchers.

Your systematic literature review will follow very clear and defined protocols that are decided on prior to any review. This involves extensive planning, and a deliberately designed search strategy that is in tune with the specific research question. Every aspect of a systematic literature review, including the research protocols, which databases are used, and dates of each search, must be transparent so that other researchers can be assured that the systematic literature review is comprehensive and focused.

Most systematic literature reviews originated in the world of medicine science. Now, they also include any evidence-based research questions. In addition to the focus and transparency of these types of reviews, additional aspects of a quality systematic literature review includes:

• Clear and concise review and summary
• Comprehensive coverage of the topic
• Accessibility and equality of the research reviewed

Systematic Review vs Literature Review

The difference between literature review and systematic review comes back to the initial research question. Whereas the systematic review is very specific and focused, the standard literature review is much more general. The components of a literature review, for example, are similar to any other research paper. That is, it includes an introduction, description of the methods used, a discussion and conclusion, as well as a reference list or bibliography.

A systematic review, however, includes entirely different components that reflect the specificity of its research question, and the requirement for transparency and inclusion. For instance, the systematic review will include:

• Eligibility criteria for included research
• A description of the systematic research search strategy
• An assessment of the validity of reviewed research
• Interpretations of the results of research included in the review

As you can see, contrary to the general overview or summary of a topic, the systematic literature review includes much more detail and work to compile than a standard literature review. Indeed, it can take years to conduct and write a systematic literature review. But the information that practitioners and other researchers can glean from a systematic literature review is, by its very nature, exceptionally valuable.

This is not to diminish the value of the standard literature review. The importance of literature reviews in research writing is discussed in this article . It’s just that the two types of research reviews answer different questions, and, therefore, have different purposes and roles in the world of research and evidence-based writing.

Systematic Literature Review vs Meta Analysis

It would be understandable to think that a systematic literature review is similar to a meta analysis. But, whereas a systematic review can include several research studies to answer a specific question, typically a meta analysis includes a comparison of different studies to suss out any inconsistencies or discrepancies. For more about this topic, check out Systematic Review VS Meta-Analysis article.

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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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Systematic Reviews

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Reproduced from Grant, M. J. and Booth, A. (2009), A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information & Libraries Journal, 26: 91–108. doi:10.1111/j.1471-1842.2009.00848.x

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A literature review is a review and synthesis of existing research on a topic or research question. A literature review is meant to analyze the scholarly literature, make connections across writings and identify strengths, weaknesses, trends, and missing conversations. A literature review should address different aspects of a topic as it relates to your research question. A literature review goes beyond a description or summary of the literature you have read. 

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Systematic Review vs. Literature Review

4-minute read

• 28th October 2023

If you’ve been reading research papers, chances are you’ve come across two commonly used approaches to synthesizing existing knowledge: systematic reviews and literature reviews. Although they share similarities, it’s important to understand their differences to help you choose the most appropriate method for your research needs.

In this blog post, we’ll outline the key distinctions between systematic reviews and literature reviews, so that you can make an informed decision about which approach to include in your research plan . Let’s begin!

Objective and Purpose

The primary objective of a literature review is to provide an overview and summary of the existing literature on a specific topic to set the stage for your own critical evaluation . A literature review aims to identify key concepts, theories, and research findings, as well as gaps in knowledge, to establish a foundation for further studies.

On the other hand, systematic reviews have a more focused purpose. They aim to address a particular research question using a predefined methodology and criteria for study selection. Systematic reviews seek to provide a comprehensive and objective summary of the available evidence in order to draw significant conclusions.

Methodology and Process

Literature reviews often adopt a flexible and iterative approach. They utilize the analysis, evaluation, and summarization of relevant research or scholarly literature, such as journal articles, books, and conference proceedings. Researchers use various search strategies and sources to gather the material; selection criteria may be loosely defined. When undertaking the literature review, qualitative techniques are often used to identify patterns and themes.

In contrast, systematic reviews follow a more structured and replicable process. After your key research question has been fully developed, it can often be helpful to follow an analytic framework to guide your research. Extensive literature searches across multiple databases are conducted using predefined search terms and strict inclusion and exclusion criteria. Researchers critically assess the quality of research and risk of bias in each study, systematically extract and analyze the data, and may employ statistical methods, such as meta-analysis , to synthesize the findings.

Outcomes and Findings

The outcomes of literature reviews primarily include a summary of the existing literature, key findings, useful methodologies, and identified research gaps . These reviews provide a broad understanding of the current state of knowledge in a particular area and can help researchers identify directions for future studies. Literature reviews aim to describe and analyze the existing research rather than providing definitive conclusions or making recommendations.

Systematic reviews, however, produce more conclusive results. They statistically analyze the data from selected studies, often incorporating meta-analysis, in order to answer the key research question. Systematic review findings often include a summary of findings table to communicate the main outcomes as well as information about the materials that were covered in the review.

Applicability and Utility

Due to their broad nature, literature reviews are useful for researchers looking to gain an overview of a specific field or topic. They provide a foundation for understanding existing knowledge, identifying gaps, and generating research questions. Literature reviews tend to be used in the early stages of research projects or when developing theoretical frameworks for a thesis or dissertation.

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With their rigorous methodology, systematic reviews are valuable for informing evidence-based practice and decision-making. They can be used as stand-alone scientific publications to illustrate the current state of scientific evidence, set a research agenda, or inform policy-making.

If you’re trying to decide whether a systematic review or literature review is the best approach for your project, consider the main distinctions:

1. Literature reviews offer a broad overview of the existing literature and identify research gaps, while systematic reviews focus on answering a specific research question.

2. Literature reviews commonly adopt a flexible and iterative approach, while systematic reviews use a structured and rigorous approach.

3. Literature reviews identify key findings, useful methodologies, and identified research gaps. Systematic reviews, on the other hand, produce conclusive results to answer the key research question.

4. Literature reviews are often carried out early on in a thesis or dissertation to identify existing research gaps, whereas systematic reviews can stand on their own as a conclusive analysis.

Once you understand these differences, you’re ready to choose the best approach for your own research paper.

And if you’re interested in getting help with proofreading your research paper, consider our research paper editing services . You can even try a sample of our services for free . Good luck reviewing and researching!

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Systematic Review vs. Literature Review: Some Essential Differences

Most budding researchers are confused between systematic review vs. literature review. As a PhD student or early career researcher, you must by now be well versed with the fact that literature review is the most important aspect of any scientific research, without which a study cannot be commenced. However, literature review is in itself an ‘umbrella term’, and there are several types of reviews, such as systematic literature reviews , that you may need to perform during your academic publishing journey, based upon their specific relevance to each study.   

Your research goal, approach, and design will finally influence your choice of systematic review vs literature review . Apart from systematic literature review , some other common types of literature review are 1 :   

• Narrative literature review – used to identify gaps in the existing knowledge base  
• Scoping literature review – used to identify the scope of a particular study  
• Integrative literature review – used to generate secondary data that upon integration can be used to define new frameworks and perspectives  
• Theoretical literature review – used to pool all kinds of theories associated with a particular concept  

The most commonly used form of review, however, is the systematic literature review . Compared to the other types of literature reviews described above, this one requires a more rigorous and well-defined approach. The systematic literature review can be divided into two main categories: meta-analysis and meta-synthesis. Meta-analysis is related to identifying patterns and relationships within the data, by using statistical procedures. Meta-synthesis on the other hand, is concerned with integrating findings of multiple qualitative research studies, not necessarily needing statistical procedures.  

Table of Contents

Difference between systematic review and literature review

In spite of having this basic understanding, however, there might still be a lot of confusion when it comes to finalizing between a systematic review vs literature review of any other kind. Since these two types of reviews serve a similar purpose, they are often used interchangeably and the difference between systematic review and literature review is overlooked.  In order to ease this confusion and smoothen the process of decision-making it is essential to have a closer look at a systematic review vs. literature review and the differences between them 2.3 :   

  Tips to keep in mind when performing a literature review  

While the above illustrated similarities and differences between systematic review and literature review might be helpful as an overview, here are some additional pointers that you can keep in mind while performing a review for your research study 4 :  

• Check the authenticity of the source thoroughly while using an article in your review.  
• Regardless of the type of review that you intend to perform, i t is important to ensure that the landmark literature, the one that first spoke about your topic of interest, is given prominence in your review. These can be identified with a simple Google Scholar search and checking the most cited articles.  
• Make sure to include all the latest literature that focuses on your research question.   
• Avoid including irrelevant data by revisiting your aims, objectives, and research questions as often as possible during the review process.  
• If you intend to submit your review in any peer-reviewed journal, make sure to have a defined structure based upon your selected type of review .  
• If it is a systematic literature review , make sure that the research question is clear and cri sp and framed in a manner that is subjected to quantitative analysis.  
• If it is a literature review of any other kind, make sure that you include enough checkpoints to minimize biases in your conclusions . You can use an integrative approach to show how different data points fit together, however, it is also essential to mention and describe data that doesn’t fit together in order to produce a balanced review. This can also help identify gaps and pave the way for designing future studies on the topic.   

We hope that the above article was helpful for you in understanding the basics of literature review and to know the use of systemic review vs. literature review.

Q: When to do a systematic review?

A systematic review is conducted to synthesize and analyze existing research on a specific question. It’s valuable when a comprehensive assessment of available evidence is required to answer a well-defined research question. Systematic reviews follow a predefined protocol, rigorous methodology, and aim to minimize bias. They’re especially useful for informing evidence-based decisions in healthcare and policy-making.

Q: When to do a literature review?

A literature review surveys existing literature on a topic, providing an overview of key concepts and findings. It’s conducted when exploring a subject, identifying gaps, and contextualizing research. Literature reviews are valuable at the beginning of a study to establish the research landscape and justify the need for new research.

Q: What is the difference between a literature review and a scoping review?

A literature review summarizes existing research on a topic, while a scoping review maps the literature to identify research gaps and areas for further investigation. While both assess existing literature, a scoping review tends to have broader inclusion criteria and aims to provide an overview of the available research, helping researchers understand the breadth of a topic before narrowing down a research question.

Q: What’ is the difference between systematic Literature Review and Meta Analysis?

A systematic literature review aims to comprehensively identify, select, and analyze all relevant studies on a specific research question using a rigorous methodology. It summarizes findings qualitatively. On the other hand, a meta-analysis is a statistical technique applied within a systematic review. It involves pooling and analyzing quantitative data from multiple studies to provide a more precise estimate of an effect size. In essence, a meta-analysis is a quantitative synthesis that goes beyond the qualitative summary of a systematic literature review.

References:  

• Types of Literature Review – Business Research Methodology. https://research-methodology.net/research-methodology/types-literature-review/  
• Mellor, L. The difference between a systematic review and a literature review. Covidence. https://www.covidence.org/blog/the-difference-between-a-systematic-review-and-a-literature-review \
• Basu, G. SJSU Research Guides – Literature Review vs Systematic Review.  https://libguides.sjsu.edu/LitRevVSSysRev/definitions  
• Jansen, D., Phair, D. Writing A Literature Review: 7 Common (And Costly) Mistakes To Avoid. Grad Coach, June 2021. https://gradcoach.com/literature-review-mistakes/  

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• Systematic Review | Definition, Example, & Guide

Systematic Review | Definition, Example & Guide

Published on June 15, 2022 by Shaun Turney . Revised on November 20, 2023.

A systematic review is a type of review that uses repeatable methods to find, select, and synthesize all available evidence. It answers a clearly formulated research question and explicitly states the methods used to arrive at the answer.

They answered the question “What is the effectiveness of probiotics in reducing eczema symptoms and improving quality of life in patients with eczema?”

In this context, a probiotic is a health product that contains live microorganisms and is taken by mouth. Eczema is a common skin condition that causes red, itchy skin.

Table of contents

What is a systematic review, systematic review vs. meta-analysis, systematic review vs. literature review, systematic review vs. scoping review, when to conduct a systematic review, pros and cons of systematic reviews, step-by-step example of a systematic review, other interesting articles, frequently asked questions about systematic reviews.

A review is an overview of the research that’s already been completed on a topic.

What makes a systematic review different from other types of reviews is that the research methods are designed to reduce bias . The methods are repeatable, and the approach is formal and systematic:

• Formulate a research question
• Develop a protocol
• Search for all relevant studies
• Apply the selection criteria
• Extract the data
• Synthesize the data
• Write and publish a report

Although multiple sets of guidelines exist, the Cochrane Handbook for Systematic Reviews is among the most widely used. It provides detailed guidelines on how to complete each step of the systematic review process.

Systematic reviews are most commonly used in medical and public health research, but they can also be found in other disciplines.

Systematic reviews typically answer their research question by synthesizing all available evidence and evaluating the quality of the evidence. Synthesizing means bringing together different information to tell a single, cohesive story. The synthesis can be narrative ( qualitative ), quantitative , or both.

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Systematic reviews often quantitatively synthesize the evidence using a meta-analysis . A meta-analysis is a statistical analysis, not a type of review.

A meta-analysis is a technique to synthesize results from multiple studies. It’s a statistical analysis that combines the results of two or more studies, usually to estimate an effect size .

A literature review is a type of review that uses a less systematic and formal approach than a systematic review. Typically, an expert in a topic will qualitatively summarize and evaluate previous work, without using a formal, explicit method.

Although literature reviews are often less time-consuming and can be insightful or helpful, they have a higher risk of bias and are less transparent than systematic reviews.

Similar to a systematic review, a scoping review is a type of review that tries to minimize bias by using transparent and repeatable methods.

However, a scoping review isn’t a type of systematic review. The most important difference is the goal: rather than answering a specific question, a scoping review explores a topic. The researcher tries to identify the main concepts, theories, and evidence, as well as gaps in the current research.

Sometimes scoping reviews are an exploratory preparation step for a systematic review, and sometimes they are a standalone project.

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A systematic review is a good choice of review if you want to answer a question about the effectiveness of an intervention , such as a medical treatment.

To conduct a systematic review, you’ll need the following:

• A precise question , usually about the effectiveness of an intervention. The question needs to be about a topic that’s previously been studied by multiple researchers. If there’s no previous research, there’s nothing to review.
• If you’re doing a systematic review on your own (e.g., for a research paper or thesis ), you should take appropriate measures to ensure the validity and reliability of your research.
• Access to databases and journal archives. Often, your educational institution provides you with access.
• Time. A professional systematic review is a time-consuming process: it will take the lead author about six months of full-time work. If you’re a student, you should narrow the scope of your systematic review and stick to a tight schedule.
• Bibliographic, word-processing, spreadsheet, and statistical software . For example, you could use EndNote, Microsoft Word, Excel, and SPSS.

A systematic review has many pros .

• They minimize research bias by considering all available evidence and evaluating each study for bias.
• Their methods are transparent , so they can be scrutinized by others.
• They’re thorough : they summarize all available evidence.
• They can be replicated and updated by others.

Systematic reviews also have a few cons .

• They’re time-consuming .
• They’re narrow in scope : they only answer the precise research question.

The 7 steps for conducting a systematic review are explained with an example.

Step 1: Formulate a research question

Formulating the research question is probably the most important step of a systematic review. A clear research question will:

• Allow you to more effectively communicate your research to other researchers and practitioners
• Guide your decisions as you plan and conduct your systematic review

A good research question for a systematic review has four components, which you can remember with the acronym PICO :

• Population(s) or problem(s)
• Intervention(s)
• Comparison(s)

You can rearrange these four components to write your research question:

• What is the effectiveness of I versus C for O in P ?

Sometimes, you may want to include a fifth component, the type of study design . In this case, the acronym is PICOT .

• Type of study design(s)
• The population of patients with eczema
• The intervention of probiotics
• In comparison to no treatment, placebo , or non-probiotic treatment
• The outcome of changes in participant-, parent-, and doctor-rated symptoms of eczema and quality of life
• Randomized control trials, a type of study design

Their research question was:

• What is the effectiveness of probiotics versus no treatment, a placebo, or a non-probiotic treatment for reducing eczema symptoms and improving quality of life in patients with eczema?

Step 2: Develop a protocol

A protocol is a document that contains your research plan for the systematic review. This is an important step because having a plan allows you to work more efficiently and reduces bias.

Your protocol should include the following components:

• Background information : Provide the context of the research question, including why it’s important.
• Research objective (s) : Rephrase your research question as an objective.
• Selection criteria: State how you’ll decide which studies to include or exclude from your review.
• Search strategy: Discuss your plan for finding studies.
• Analysis: Explain what information you’ll collect from the studies and how you’ll synthesize the data.

If you’re a professional seeking to publish your review, it’s a good idea to bring together an advisory committee . This is a group of about six people who have experience in the topic you’re researching. They can help you make decisions about your protocol.

It’s highly recommended to register your protocol. Registering your protocol means submitting it to a database such as PROSPERO or ClinicalTrials.gov .

Step 3: Search for all relevant studies

Searching for relevant studies is the most time-consuming step of a systematic review.

To reduce bias, it’s important to search for relevant studies very thoroughly. Your strategy will depend on your field and your research question, but sources generally fall into these four categories:

• Databases: Search multiple databases of peer-reviewed literature, such as PubMed or Scopus . Think carefully about how to phrase your search terms and include multiple synonyms of each word. Use Boolean operators if relevant.
• Handsearching: In addition to searching the primary sources using databases, you’ll also need to search manually. One strategy is to scan relevant journals or conference proceedings. Another strategy is to scan the reference lists of relevant studies.
• Gray literature: Gray literature includes documents produced by governments, universities, and other institutions that aren’t published by traditional publishers. Graduate student theses are an important type of gray literature, which you can search using the Networked Digital Library of Theses and Dissertations (NDLTD) . In medicine, clinical trial registries are another important type of gray literature.
• Experts: Contact experts in the field to ask if they have unpublished studies that should be included in your review.

At this stage of your review, you won’t read the articles yet. Simply save any potentially relevant citations using bibliographic software, such as Scribbr’s APA or MLA Generator .

• Databases: EMBASE, PsycINFO, AMED, LILACS, and ISI Web of Science
• Handsearch: Conference proceedings and reference lists of articles
• Gray literature: The Cochrane Library, the metaRegister of Controlled Trials, and the Ongoing Skin Trials Register
• Experts: Authors of unpublished registered trials, pharmaceutical companies, and manufacturers of probiotics

Step 4: Apply the selection criteria

Applying the selection criteria is a three-person job. Two of you will independently read the studies and decide which to include in your review based on the selection criteria you established in your protocol . The third person’s job is to break any ties.

To increase inter-rater reliability , ensure that everyone thoroughly understands the selection criteria before you begin.

If you’re writing a systematic review as a student for an assignment, you might not have a team. In this case, you’ll have to apply the selection criteria on your own; you can mention this as a limitation in your paper’s discussion.

You should apply the selection criteria in two phases:

• Based on the titles and abstracts : Decide whether each article potentially meets the selection criteria based on the information provided in the abstracts.
• Based on the full texts: Download the articles that weren’t excluded during the first phase. If an article isn’t available online or through your library, you may need to contact the authors to ask for a copy. Read the articles and decide which articles meet the selection criteria.

It’s very important to keep a meticulous record of why you included or excluded each article. When the selection process is complete, you can summarize what you did using a PRISMA flow diagram .

Next, Boyle and colleagues found the full texts for each of the remaining studies. Boyle and Tang read through the articles to decide if any more studies needed to be excluded based on the selection criteria.

When Boyle and Tang disagreed about whether a study should be excluded, they discussed it with Varigos until the three researchers came to an agreement.

Step 5: Extract the data

Extracting the data means collecting information from the selected studies in a systematic way. There are two types of information you need to collect from each study:

• Information about the study’s methods and results . The exact information will depend on your research question, but it might include the year, study design , sample size, context, research findings , and conclusions. If any data are missing, you’ll need to contact the study’s authors.
• Your judgment of the quality of the evidence, including risk of bias .

You should collect this information using forms. You can find sample forms in The Registry of Methods and Tools for Evidence-Informed Decision Making and the Grading of Recommendations, Assessment, Development and Evaluations Working Group .

Extracting the data is also a three-person job. Two people should do this step independently, and the third person will resolve any disagreements.

They also collected data about possible sources of bias, such as how the study participants were randomized into the control and treatment groups.

Step 6: Synthesize the data

Synthesizing the data means bringing together the information you collected into a single, cohesive story. There are two main approaches to synthesizing the data:

• Narrative ( qualitative ): Summarize the information in words. You’ll need to discuss the studies and assess their overall quality.
• Quantitative : Use statistical methods to summarize and compare data from different studies. The most common quantitative approach is a meta-analysis , which allows you to combine results from multiple studies into a summary result.

Generally, you should use both approaches together whenever possible. If you don’t have enough data, or the data from different studies aren’t comparable, then you can take just a narrative approach. However, you should justify why a quantitative approach wasn’t possible.

Boyle and colleagues also divided the studies into subgroups, such as studies about babies, children, and adults, and analyzed the effect sizes within each group.

Step 7: Write and publish a report

The purpose of writing a systematic review article is to share the answer to your research question and explain how you arrived at this answer.

Your article should include the following sections:

• Abstract : A summary of the review
• Introduction : Including the rationale and objectives
• Methods : Including the selection criteria, search method, data extraction method, and synthesis method
• Results : Including results of the search and selection process, study characteristics, risk of bias in the studies, and synthesis results
• Discussion : Including interpretation of the results and limitations of the review
• Conclusion : The answer to your research question and implications for practice, policy, or research

To verify that your report includes everything it needs, you can use the PRISMA checklist .

Once your report is written, you can publish it in a systematic review database, such as the Cochrane Database of Systematic Reviews , and/or in a peer-reviewed journal.

In their report, Boyle and colleagues concluded that probiotics cannot be recommended for reducing eczema symptoms or improving quality of life in patients with eczema. Note Generative AI tools like ChatGPT can be useful at various stages of the writing and research process and can help you to write your systematic review. However, we strongly advise against trying to pass AI-generated text off as your own work.

If you want to know more about statistics , methodology , or research bias , make sure to check out some of our other articles with explanations and examples.

• Student’s  t -distribution
• Normal distribution
• Null and Alternative Hypotheses
• Chi square tests
• Confidence interval
• Quartiles & Quantiles
• Cluster sampling
• Stratified sampling
• Data cleansing
• Reproducibility vs Replicability
• Peer review
• Prospective cohort study

Research bias

• Implicit bias
• Cognitive bias
• Placebo effect
• Hawthorne effect
• Hindsight bias
• Affect heuristic
• Social desirability bias

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.

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

A systematic review is secondary research because it uses existing research. You don’t collect new data yourself.

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Research Methods

• Getting Started
• Literature Review Research
• Research Design
• Research Design By Discipline
• SAGE Research Methods
• Teaching with SAGE Research Methods

Literature Review

• What is a Literature Review?
• What is NOT a Literature Review?
• Purposes of a Literature Review
• Types of Literature Reviews
• Literature Reviews vs. Systematic Reviews
• Systematic vs. Meta-Analysis

Literature Review  is a comprehensive survey of the works published in a particular field of study or line of research, usually over a specific period of time, in the form of an in-depth, critical bibliographic essay or annotated list in which attention is drawn to the most significant works.

Also, we can define a literature review as the collected body of scholarly works related to a topic:

• Summarizes and analyzes previous research relevant to a topic
• Includes scholarly books and articles published in academic journals
• Can be an specific scholarly paper or a section in a research paper

The objective of a Literature Review is to find previous published scholarly works relevant to an specific topic

• Help gather ideas or information
• Keep up to date in current trends and findings
• Help develop new questions

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Helps focus your own research questions or problems
• Discovers relationships between research studies/ideas.
• Suggests unexplored ideas or populations
• Identifies major themes, concepts, and researchers on a topic.
• Tests assumptions; may help counter preconceived ideas and remove unconscious bias.
• Identifies critical gaps, points of disagreement, or potentially flawed methodology or theoretical approaches.
• Indicates potential directions for future research.

All content in this section is from Literature Review Research from Old Dominion University 

Keep in mind the following, a literature review is NOT:

Not an essay 

Not an annotated bibliography  in which you summarize each article that you have reviewed.  A literature review goes beyond basic summarizing to focus on the critical analysis of the reviewed works and their relationship to your research question.

Not a research paper   where you select resources to support one side of an issue versus another.  A lit review should explain and consider all sides of an argument in order to avoid bias, and areas of agreement and disagreement should be highlighted.

A literature review serves several purposes. For example, it

• provides thorough knowledge of previous studies; introduces seminal works.
• helps focus one’s own research topic.
• identifies a conceptual framework for one’s own research questions or problems; indicates potential directions for future research.
• suggests previously unused or underused methodologies, designs, quantitative and qualitative strategies.
• identifies gaps in previous studies; identifies flawed methodologies and/or theoretical approaches; avoids replication of mistakes.
• helps the researcher avoid repetition of earlier research.
• suggests unexplored populations.
• determines whether past studies agree or disagree; identifies controversy in the literature.
• tests assumptions; may help counter preconceived ideas and remove unconscious bias.

As Kennedy (2007) notes*, it is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the original studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally that become part of the lore of field. In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews.

Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are several approaches to how they can be done, depending upon the type of analysis underpinning your study. Listed below are definitions of types of literature reviews:

Argumentative Review      This form examines literature selectively in order to support or refute an argument, deeply imbedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to to make summary claims of the sort found in systematic reviews.

Integrative Review      Considered 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. The body of literature includes all studies that address related or identical hypotheses. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication.

Historical Review      Few things rest in isolation from historical precedent. Historical reviews are focused on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review      A review does not always focus on what someone said [content], but how they said it [method of analysis]. This approach provides a framework of understanding at different levels (i.e. those of theory, substantive fields, research approaches and data collection and analysis techniques), enables researchers to draw on a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection and data analysis, and helps highlight many ethical issues which we should be aware of and consider as we go through our study.

Systematic Review      This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyse data from the studies that are included in the review. Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?"

Theoretical Review      The purpose of this form is to concretely examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review help establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

* Kennedy, Mary M. "Defining a Literature."  Educational Researcher  36 (April 2007): 139-147.

All content in this section is from The Literature Review created by Dr. Robert Larabee USC

Robinson, P. and Lowe, J. (2015),  Literature reviews vs systematic reviews.  Australian and New Zealand Journal of Public Health, 39: 103-103. doi: 10.1111/1753-6405.12393

What's in the name? The difference between a Systematic Review and a Literature Review, and why it matters . By Lynn Kysh from University of Southern California

Systematic review or meta-analysis?

A  systematic review  answers a defined research question by collecting and summarizing all empirical evidence that fits pre-specified eligibility criteria.

A  meta-analysis  is the use of statistical methods to summarize the results of these studies.

Systematic reviews, just like other research articles, can be of varying quality. They are a significant piece of work (the Centre for Reviews and Dissemination at York estimates that a team will take 9-24 months), and to be useful to other researchers and practitioners they should have:

• clearly stated objectives with pre-defined eligibility criteria for studies
• explicit, reproducible methodology
• a systematic search that attempts to identify all studies
• assessment of the validity of the findings of the included studies (e.g. risk of bias)
• systematic presentation, and synthesis, of the characteristics and findings of the included studies

Not all systematic reviews contain meta-analysis. 

Meta-analysis is the use of statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analysis can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review.  More information on meta-analyses can be found in  Cochrane Handbook, Chapter 9 .

A meta-analysis goes beyond critique and integration and conducts secondary statistical analysis on the outcomes of similar studies.  It is a systematic review that uses quantitative methods to synthesize and summarize the results.

An advantage of a meta-analysis is the ability to be completely objective in evaluating research findings.  Not all topics, however, have sufficient research evidence to allow a meta-analysis to be conducted.  In that case, an integrative review is an appropriate strategy. 

Some of the content in this section is from Systematic reviews and meta-analyses: step by step guide created by Kate McAllister.

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• University Libraries
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• Reviewing Research: Literature Reviews, Scoping Reviews, Systematic Reviews
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Reviewing Research: Literature Reviews, Scoping Reviews, Systematic Reviews: Differentiating the Three Review Types

• Framework, Protocol, and Writing Steps
• Working with Keywords/Subject Headings
• Citing Research

The Differences in the Review Types

Grant, M.J. and Booth, A. (2009), A typology of reviews: an analysis of 14 review types and associated methodologies. H ealth Information & Libraries Journal , 26: 91-108. https://doi.org/10.1111/j.1471-1842.2009.00848.x   The objective of this study is to provide descriptive insight into the most common types of reviews, with illustrative examples from health and health information domains.

• What Type of Review is Right for you (Cornell University)

Literature Reviews

Literature Review: it is a product and a process.

As a product , it is a carefully written examination, interpretation, evaluation, and synthesis of the published literature related to your topic. It focuses on what is known about your topic and what methodologies, models, theories, and concepts have been applied to it by others.

The process is what is involved in conducting a review of the literature.

• It is ongoing
• It is iterative (repetitive)
• It involves searching for and finding relevant literature.
• It includes keeping track of your references and preparing and formatting them for the bibliography of your thesis

• Literature Reviews (University of North Carolina at Chapel Hill) This handout will explain what literature reviews are and offer insights into the form and construction of literature reviews in the humanities, social sciences, and sciences.

Scoping Reviews

Scoping reviews are a " preliminary assessment of potential size and scope of available research literature . Aims to identify nature and extent of research evidence (usually including ongoing research)." Grant and Booth (2009).

Scoping reviews are not mapping reviews: Scoping reviews are more topic based and mapping reviews are more question based.

• examining emerging evidence when specific questions are unclear - clarify definitions and conceptual boundaries
• identify and map the available evidence
• a scoping review is done prior to a systematic review
• to summarize and disseminate research findings in the research literature
• identify gaps with the intention of resolution by future publications

• Scoping review timeframe and limitations (Touro College of Pharmacy

Systematic Reviews

Many evidence-based disciplines use ‘systematic reviews," this type of review is a specific methodology that aims to comprehensively identify all relevant studies on a specific topic, and to select appropriate studies based on explicit criteria . ( https://cebma.org/faq/what-is-a-systematic-review/ )

• clearly defined search criteria
• an explicit reproducible methodology
• a systematic search of the literature with the defined criteria met
• assesses validity of the findings - no risk of bias
• a comprehensive report on the findings, apparent transparency in the results

• Better evidence for a better world Browsable collection of systematic reviews
• Systematic Reviews in the Health Sciences by Molly Maloney Last Updated Jul 26, 2024 850 views this year
• Next: Framework, Protocol, and Writing Steps >>

Literature Review Research

Literature review vs. systematic review.

• Literature Review Process
• Finding Literature Reviews
• Helpful Tips and Resources
• Citing Sources This link opens in a new window

Resources for Systematic Reviews

• NIH Systematic Review Protocols and Protocol Registries Systematic review services and information from the National Institutes of Health.
• Purdue University Systematic Reviews LibGuide Purdue University has created this helpful online research guide on systematic reviews. Most content is available publicly but please note that some links are accessible only to Purdue students.

It is common to confuse literature and systematic reviews because both are used to provide a summary of the existing literature or research on a specific topic. Despite this commonality, these two reviews vary significantly. The table below highlights the differences.

Kysh, Lynn (2013). Difference between a systematic review and a literature review. figshare. Poster. https://doi.org/10.6084/m9.figshare.766364.v1

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Literature Review vs Research Paper: What’s the Difference?

by  Antony W

June 26, 2024

This is a complete student’s guide to understanding literature review vs research paper.

We’ll teach you what they’re, explain why they’re important, state the difference between the two, and link you to our comprehensive guide on how to write them.

Literature Review Writing Help

Writing a literature review for a thesis, a research paper, or as a standalone assignment takes time. Much of your time will go into research, not to mention you have other assignments to complete. 

If you find writing in college or university overwhelming, get in touch with our literature review writers for hire at 25% discounts and enjoy the flexibility and convenience that comes with professional writing help. We’ll help you do everything, from research and outlining to custom writing and proofreading.

What is a Literature Review?

A literature review document is a secondary source of information that provides an overview of existing knowledge, which you can use to identify gaps or flaws in existing research. In literature review writing, students have to find and read existing publications such as journal articles, analyze the information, and then state their findings.

Credit: Pubrica

You’ll write a literature review to demonstrate your understanding on the topic, show gaps in existing research, and develop an effective methodology and a theoretical framework for your research project.

Your instructor may ask you to write a literature review as a standalone assignment. Even if that’s the case, the rules for writing a review paper don’t change.

In other words, you’ll still focus on evaluating the current research and find gaps around the topic.

Types of Literature Reviews

There are three types of review papers and they’re a follows:

 1. Meta-analysis

In meta-analysis review paper, you combine and compare answers from already published studies on a given subject.

2. Narrative Review

A narrative review paper looks into existing information or research already conducted on a given topic.

3. Systematic Review

You need to do three things if asked to write a systematic review paper.

First, read and understand the question asked. Second, look into research already conducted on the topic. Third, search for the answer to the question from the established research you just read.

What’s a Research Paper?

A research paper is an assignment in which you present your own argument, evaluation, or interpretation of an issue based on independent research.

In a research paper project, you’ll draw some conclusions from what experts have already done, find gaps in their studies, and then draw your own conclusions.

While a research paper is like an academic essay, it tends to be longer and more detailed.

Since they require extended research and attention to details, research papers can take a lot of time to write.

If well researched, your research paper can demonstrate your knowledge about a topic, your ability to engage with multiple sources, and your willingness to contribute original thoughts to an ongoing debate.

Types of Research Papers

 There are two types of research papers and they’re as follows:

 1. Analytical Research Papers

 Similar to analytical essay , and usually in the form of a question, an analytical research paper looks at an issue from a neutral point and gives a clear analysis of the issue.

Your goal is to make the reader understand both sides of the issue in question and leave it to them to decide what side of the analysis to accept.

Unlike an argumentative research paper, an analytical research paper doesn’t include counterarguments. And you can only draw your conclusion based on the information stretched out all through the analysis.

2. Argumentative Research Papers

In an argumentative research paper, you state the subject under study, look into both sides of an issue, pick a stance, and then use solid evidence and objective reasons to defend your position.

In   argumentative writing, your goal isn’t to persuade your audience to take an action. 

Rather, it’s to convince them that your position on the research question is more accurate than the opposing point of views.

Regardless of the type of research paper that you write, you’ll have to follow the standard outline for the assignment to be acceptable for review and marking.

Also, all research paper, regardless of the research question under investigation must include a literature review.

Literature Review vs Research Paper

The table below shows the differences between a literature review (review paper) and a research paper. 

Frequently Asked Questions

1. is there a literature review in a research paper.

A research paper assignment must include a literature review immediately after the introduction chapter.

The chapter is significant because your research work would otherwise be incomplete without knowledge of existing literature. 

2. How Many Literature Review Should Be in Research Paper?

Your research paper  should have only one literature review. Make sure you write the review based on the instructions from your teacher.

Before you start, check the required length, number of sources to summarize, and the format to use. Doing so will help you score top grades for the assignment. 

3. What is the Difference Between Research and Literature?

Whereas literature focuses on gathering, reading, and summarizing information on already established studies, original research involves coming up with new concepts, theories, and ideas that might fill existing gaps in the available literature.

4. How Long is a Literature Review?

How long a literature review should be will depend on several factors, including the level of education, the length of the assignment, the target audience, and the purpose of the review.

For example, a 150-page dissertation can have a literature review of 40 pages on average.

Make sure you talk to your instructor to determine the required length of the assignment.

5. How Does a Literature Review Look Like?

Your literature review shouldn’t be a focus on original research or new information. Rather, it should give a clear overview of the already existing work on the selected topic.

The information to review can come from various sources, including scholarly journal articles , government reports, credible websites, and academic-based books. 

About the author 

Antony W is a professional writer and coach at Help for Assessment. He spends countless hours every day researching and writing great content filled with expert advice on how to write engaging essays, research papers, and assignments.

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Know the Difference! Systematic Review vs. Literature Review

It is common to confuse systematic and literature reviews as both are used to provide a summary of the existent literature or research on a specific topic.  Even with this common ground, both types vary significantly.  Please review the following chart (and its corresponding poster linked below) for the detailed explanation of each as well as the differences between each type of review.

• What's in a name? The difference between a Systematic Review and a Literature Review, and why it matters by Lynn Kysh, MLIS, University of Southern California - Norris Medical Library
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Common Paper Types

• Literature Review
• Scoping Review
• Systematic Review
• Author Profile

Understanding Literature Reviews 

I.  Getting Started with a Workshop Video  (Highly recommended!)

• Searching for Literature Reviews: Before You Write, You Have to Find   https://www.youtube.com/watch?v=9la5ytz9MmM

          A lecture by the Writing Center, TAMU.

II.  What is a Literature Review?

• Generally, the purpose of a review is to analyze critically a segment of a published body of knowledge through summary, classification, and comparison of prior research studies, reviews of literature, and theoretical articles. <http://writing.wisc.edu/Handbook/ReviewofLiterature.html>  
•  A literature review can be just a simple summary of the sources, but it usually has an organizational pattern and combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.  < http://writingcenter.unc.edu/resources/handouts-demos/specific-writing-assignments/literature-reviews >  
•  A literature review is a body of text that aims to review the critical points of current knowledge including substantive findings as well as theoretical and methodological contributions to a particular topic...Its ultimate goal is to bring the reader up to date with current literature on a topic and forms the basis for another goal, such as future research that may be needed in the area. <http://en.wikipedia.org/wiki/Literature_review>

III.  What Major Steps Literature Reviews Require?

• 1. Develop a review protocol. Protocols define the scope of studies that will be reviewed, the process through which studies will be identified, and the outcomes that will be examined. Protocols also specify the time period during which relevant studies will have been conducted, the outcomes to be examined in the review, and keyword strategies for the literature search. 2. Identify relevant studies, often through a systematic search of the literature. 3. Screen studies for relevance and the adequacy of study design, implementation, and reporting. 4. Retrieve and summarize information on the intervention studied, the study characteristics, and the study findings. 5. Combine findings within studies and across studies when relevant. < http://ies.ed.gov/ncee/wwc/pdf/reference_resources/wwc_procedures_v2_1_standards_handbook.pdf>  
• The basic stages in a typical research project are: i) identify your topic of interest, ii) perform a literature review, iii) generate related questions, iv) state your unsolved problem or hypothesis, v) find or develop a solution, and vi) document your results.  
• The four stages required: Problem formulation—which topic or field is being examined and what are its component issues? Literature search—finding materials relevant to the subject being explored Data evaluation—determining which literature makes a significant contribution to the understanding of the topic Analysis and interpretation—discussing the findings and conclusions of pertinent literature < http://library.ucsc.edu/help/howto/write-a-literature-review#components >

IV.    What Basic Elements Comprise a Literature Review?   

• An overview of the subject, issue or theory under consideration, along with the objectives of the literature review
• Division of works under review into categories (e.g. those in support of a particular position, those against, and those offering alternative theses entirely)
• Explanation of how each work is similar to and how it varies from the others
• Conclusions as to which pieces are best considered in their argument, are most convincing of their opinions, and make the greatest contribution to the understanding and development of their area of research    

          < http://library.ucsc.edu/help/howto/write-a-literature-review#components > V.    Which Citation Tool Are You Going to Use to Manage the Search Results?

•   Choose your citation tool before conducing your literature reviews. If you decide to use  RefWorks , the information can be found at  http://tamu.libguides.com/refworks .          

VII. Other Useful Guides

• Literature Reviews (University of North Carolina at Chapel Hill)
• The Literature Review: A Few Tips On Conducting It
• How to Write a Literature Review  (UCSC)
• Learn how to write a review of literature  (WISC)
• Reviewing the Literature
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• Last Updated: Aug 5, 2024 7:43 AM
• URL: https://tamu.libguides.com/c.php?g=1415100

Basic Research Strategies for the Social Sciences: Systematic Reviews vs. Literature Reviews

• Research Strategies
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Systematic Reviews - What to Consider

Before you Begin: 

• Did you know, it takes an average of 18 months to complete a systematic review?
• Did you know that it's recommended to have at least 3 people on a systematic review team? 
• Did you know that a systematic review answers a very specific type of research question? Is your question a good fit for a systematic review? 

Contact your librarian, Emily Hart , to learn more about systematic reviews. 

Systematic Review vs. Literature Review - What's the Difference?

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"PROSPERO is an international database of prospectively registered systematic reviews in health and social care, welfare, public health, education, crime, justice, and international development, where there is a health related outcome." (Website- About)

Conducting a Literature Review

• The Literature Review (25 minutes Video - opens in a new window)) This in-depth video lecture explains how to write a Literature Review, and examines which elements are required in one. This video was created the Student Learning Centre at Massey University, Auckland.
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Literature Review vs Systematic Review

Literature review vs. systematic review, your librarian.

It’s common to confuse systematic and literature reviews because both are used to provide a summary of the existent literature or research on a specific topic. Regardless of this commonality, both types of review vary significantly. The following table provides a detailed explanation as well as the differences between systematic and literature reviews. 

Kysh, Lynn (2013): Difference between a systematic review and a literature review. [figshare]. Available at:  http://dx.doi.org/10.6084/m9.figshare.766364

Primary vs. Secondary Research

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Systematic Reviews in the Social Sciences

Types of reviews.

• What is a Systematic Review?

Literature Review vs. Systematic Review

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Reviews can have different structures and goals. The primary forms of reviews in our discipline are literature reviews and systematic reviews:

A  literature review  provides a reader with a critical overview of the sources relevant to a specific research subject, question, or idea. In writing a literature review, it is important to contextualize each resource, evaluate the content, and provide a critical analysis of the strengths, contributions, and issues.

A guide to writing literature reviews is available  here.

A  systematic review  uses a specific methodology to identify all relevant studies on a specific topic and then select appropriate studies based on very specific criteria for inclusion/exclusion. By having transparent frameworks, systematic reviews seek to be verifiable and reproducible. Systematic reviews in the discipline can often include statistical analysis techniques.

A guide to writing systematic reviews is available  here.  

A comprehensive list of all the types of reviews you might encounter as a social science researcher and their search strategies is available  here.

The following chart can guide you through deciding if a literature review or systematic review is right for you. This is available to download or print by clicking below:

Difference Between Literature Review and Systematic Review

Adopted and reformatted for social science analysis purposes from: Kysh, Lynn (2013):  Difference between a systematic review and a literature review . Figshare. https://doi.org/10.6084/m9.figshare.766364.v1

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Reviewing literature for research: Doing it the right way

Shital amin poojary.

Department of Dermatology, K J Somaiya Medical College, Mumbai, Maharashtra, India

Jimish Deepak Bagadia

In an era of information overload, it is important to know how to obtain the required information and also to ensure that it is reliable information. Hence, it is essential to understand how to perform a systematic literature search. This article focuses on reliable literature sources and how to make optimum use of these in dermatology and venereology.

INTRODUCTION

A thorough review of literature is not only essential for selecting research topics, but also enables the right applicability of a research project. Most importantly, a good literature search is the cornerstone of practice of evidence based medicine. Today, everything is available at the click of a mouse or at the tip of the fingertips (or the stylus). Google is often the Go-To search website, the supposed answer to all questions in the universe. However, the deluge of information available comes with its own set of problems; how much of it is actually reliable information? How much are the search results that the search string threw up actually relevant? Did we actually find what we were looking for? Lack of a systematic approach can lead to a literature review ending up as a time-consuming and at times frustrating process. Hence, whether it is for research projects, theses/dissertations, case studies/reports or mere wish to obtain information; knowing where to look, and more importantly, how to look, is of prime importance today.

Literature search

Fink has defined research literature review as a “systematic, explicit and reproducible method for identifying, evaluating, and synthesizing the existing body of completed and recorded work produced by researchers, scholars and practitioners.”[ 1 ]

Review of research literature can be summarized into a seven step process: (i) Selecting research questions/purpose of the literature review (ii) Selecting your sources (iii) Choosing search terms (iv) Running your search (v) Applying practical screening criteria (vi) Applying methodological screening criteria/quality appraisal (vii) Synthesizing the results.[ 1 ]

This article will primarily concentrate on refining techniques of literature search.

Sources for literature search are enumerated in Table 1 .

Sources for literature search

PubMed is currently the most widely used among these as it contains over 23 million citations for biomedical literature and has been made available free by National Center for Biotechnology Information (NCBI), U.S. National Library of Medicine. However, the availability of free full text articles depends on the sources. Use of options such as advanced search, medical subject headings (MeSH) terms, free full text, PubMed tutorials, and single citation matcher makes the database extremely user-friendly [ Figure 1 ]. It can also be accessed on the go through mobiles using “PubMed Mobile.” One can also create own account in NCBI to save searches and to use certain PubMed tools.

PubMed home page showing location of different tools which can be used for an efficient literature search

Tips for efficient use of PubMed search:[ 2 , 3 , 4 ]

Use of field and Boolean operators

When one searches using key words, all articles containing the words show up, many of which may not be related to the topic. Hence, the use of operators while searching makes the search more specific and less cumbersome. Operators are of two types: Field operators and Boolean operators, the latter enabling us to combine more than one concept, thereby making the search highly accurate. A few key operators that can be used in PubMed are shown in Tables ​ Tables2 2 and ​ and3 3 and illustrated in Figures ​ Figures2 2 and ​ and3 3 .

Field operators used in PubMed search

Boolean operators used in PubMed search

PubMed search results page showing articles on donovanosis using the field operator [TIAB]; it shows all articles which have the keyword “donovanosis” in either title or abstract of the article

PubMed search using Boolean operators ‘AND’, ‘NOT’; To search for articles on treatment of lepra reaction other than steroids, after clicking the option ‘Advanced search’ on the home page, one can build the search using ‘AND’ option for treatment and ‘NOT’ option for steroids to omit articles on steroid treatment in lepra reaction

Use of medical subject headings terms

These are very specific and standardized terms used by indexers to describe every article in PubMed and are added to the record of every article. A search using MeSH will show all articles about the topic (or keywords), but will not show articles only containing these keywords (these articles may be about an entirely different topic, but still may contain your keywords in another context in any part of the article). This will make your search more specific. Within the topic, specific subheadings can be added to the search builder to refine your search [ Figure 4 ]. For example, MeSH terms for treatment are therapy and therapeutics.

PubMed search using medical subject headings (MeSH) terms for management of gonorrhea. Click on MeSH database ( Figure 1 ) →In the MeSH search box type gonorrhea and click search. Under the MeSH term gonorrhea, there will be a list of subheadings; therapy, prevention and control, click the relevant check boxes and add to search builder →Click on search →All articles on therapy, prevention and control of gonorrhea will be displayed. Below the subheadings, there are two options: (1) Restrict to medical subject headings (MeSH) major topic and (2) do not include MeSH terms found below this term in the MeSH hierarchy. These can be used to further refine the search results so that only articles which are majorly about treatment of gonorrhea will be displayed

Two additional options can be used to further refine MeSH searches. These are located below the subheadings for a MeSH term: (1) Restrict to MeSH major topic; checking this box will retrieve articles which are majorly about the search term and are therefore, more focused and (2) Do not include MeSH terms found below this term in the MeSH hierarchy. This option will again give you more focused articles as it excludes the lower specific terms [ Figure 4 ].

Similar feature is available with Cochrane library (also called MeSH), EMBASE (known as EMTREE) and PsycINFO (Thesaurus of Psychological Index Terms).

Saving your searches

Any search that one has performed can be saved by using the ‘Send to’ option and can be saved as a simple word file [ Figure 5 ]. Alternatively, the ‘Save Search’ button (just below the search box) can be used. However, it is essential to set up an NCBI account and log in to NCBI for this. One can even choose to have E-mail updates of new articles in the topic of interest.

Saving PubMed searches. A simple option is to click on the dropdown box next to ‘Send to’ option and then choose among the options. It can be saved as a text or word file by choosing ‘File’ option. Another option is the “Save search” option below the search box but this will require logging into your National Center for Biotechnology Information account. This however allows you to set up alerts for E-mail updates for new articles

Single citation matcher

This is another important tool that helps to find the genuine original source of a particular research work (when few details are known about the title/author/publication date/place/journal) and cite the reference in the most correct manner [ Figure 6 ].

Single citation matcher: Click on “Single citation matcher” on PubMed Home page. Type available details of the required reference in the boxes to get the required citation

Full text articles

In any search clicking on the link “free full text” (if present) gives you free access to the article. In some instances, though the published article may not be available free, the author manuscript may be available free of charge. Furthermore, PubMed Central articles are available free of charge.

Managing filters

Filters can be used to refine a search according to type of article required or subjects of research. One can specify the type of article required such as clinical trial, reviews, free full text; these options are available on a typical search results page. Further specialized filters are available under “manage filters:” e.g., articles confined to certain age groups (properties option), “Links” to other databases, article specific to particular journals, etc. However, one needs to have an NCBI account and log in to access this option [ Figure 7 ].

Managing filters. Simple filters are available on the ‘search results’ page. One can choose type of article, e.g., clinical trial, reviews etc. Further options are available in the “Manage filters” option, but this requires logging into National Center for Biotechnology Information account

The Cochrane library

Although reviews are available in PubMed, for systematic reviews and meta-analysis, Cochrane library is a much better resource. The Cochrane library is a collection of full length systematic reviews, which can be accessed for free in India, thanks to Indian Council of Medical Research renewing the license up to 2016, benefitting users all over India. It is immensely helpful in finding detailed high quality research work done in a particular field/topic [ Figure 8 ].

Cochrane library is a useful resource for reliable, systematic reviews. One can choose the type of reviews required, including trials

An important tool that must be used while searching for research work is screening. Screening helps to improve the accuracy of search results. It is of two types: (1) Practical: To identify a broad range of potentially useful studies. Examples: Date of publication (last 5 years only; gives you most recent updates), participants or subjects (humans above 18 years), publication language (English only) (2) methodological: To identify best available studies (for example, excluding studies not involving control group or studies with only randomized control trials).

Selecting the right quality of literature is the key to successful research literature review. The quality can be estimated by what is known as “The Evidence Pyramid.” The level of evidence of references obtained from the aforementioned search tools are depicted in Figure 9 . Systematic reviews obtained from Cochrane library constitute level 1 evidence.

Evidence pyramid: Depicting the level of evidence of references obtained from the aforementioned search tools

Thus, a systematic literature review can help not only in setting up the basis of a good research with optimal use of available information, but also in practice of evidence-based medicine.

Source of Support: Nil.

Conflict of Interest: None declared.

Scoping Review vs Systematic Review

Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

Learn about our Editorial Process

Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

• Systematic reviews are designed to answer specific research questions with the goal of synthesizing evidence to inform clinical practice or policy decisions, such as determining the effectiveness of an intervention.
• Scoping reviews are valuable tools for exploring broader research landscapes, clarifying concepts, and identifying research gaps.

How to Choose the Best Review for your Research Topic

The Cochrane Handbook states that the primary factor in deciding between a systematic review and a scoping review is the authors’ intention:

Do they aim to use the review’s results to answer a clinically meaningful question or to inform practice?

A systematic review is recommended if the objective is to evaluate the feasibility, appropriateness, meaningfulness, or effectiveness of a treatment or practice.

For example, “Is treatment A more effective than treatment B for condition C in population D?”

The goal is to produce a comprehensive, unbiased summary of the available evidence that can be directly applied to clinical decision-making.

Systematic reviews can address various aspects of healthcare beyond just effectiveness, including patient experiences and economic considerations.

They are often the foundation for developing evidence-based clinical practice guidelines.

Conversely, a scoping review is suitable when the focus is on identifying and discussing specific characteristics or concepts within the literature rather than generating direct clinical or policy recommendations.

Scoping reviews can be an excellent way for postgraduate students to gain a broad understanding of a field or to identify potential areas for more in-depth research.

If a research area has inconsistent terminology or definitions, a scoping review can map out how different concepts are used and potentially propose a unified understanding. This can help refine the focus and scope of a subsequent systematic review.

Key differences:

• Systematic reviews aim to answer a specific question and typically involve a more rigorous, comprehensive search and analysis of the literature, including a detailed quality assessment of included studies.
• Scoping reviews aim to map the key concepts and types of evidence available on a topic. While they follow a systematic approach, they typically do not include the same level of critical appraisal as systematic reviews.
• Scoping reviews often have broader, more exploratory objectives than the focused question(s) in systematic reviews.
• Scoping reviews map the available evidence, while systematic reviews synthesize and evaluate the evidence.
• Scoping reviews typically use narrative synthesis, while systematic reviews may include meta-analysis.
• Scoping reviews often identify research gaps, while systematic reviews focus on informing practice and policy.
• Unlike scoping reviews, systematic reviews aim to be exhaustive within their defined scope, capturing all relevant evidence on a particular question.
• Critical appraisal of individual studies is optional in scoping reviews but essential in systematic reviews.
• Scoping reviews can be used as a preliminary step to a systematic review , helping to identify the types of evidence available, potential research questions, and relevant inclusion criteria.
• Due to their rigorous methodology, systematic reviews are generally more time-consuming, often taking 12-24 months to complete, while scoping reviews can usually be completed more rapidly, typically within 2-6 months.

If the goal is to determine the effectiveness of an intervention :

Systematic reviews evaluate the effectiveness of a particular intervention for a specific condition while scoping reviews map the research landscape by:

• Examining the range of interventions for a health condition.
• Identifying types of studies conducted.
• Noting populations studied.
• Summarizing outcomes measured.

Scoping reviews help identify areas needing further research, whereas systematic reviews aim to draw conclusions about intervention effectiveness.

Standardized Reporting Guidelines

The PRISMA ( Preferred Reporting Items for Systematic Reviews and Meta-Analyses ) checklist is tailored for reporting systematic reviews and meta-analyses.

It consists of 27 items covering aspects such as the rationale, objectives, eligibility criteria, search strategy, study selection process, data extraction methods, risk of bias assessment, data synthesis, and reporting of finding.

PRISMA helps researchers communicate their methods and findings more effectively, ultimately improving the reliability and usefulness of systematic reviews for informing healthcare decisions.

The PRISMA-ScR ( Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews ) checklist builds upon the PRISMA checklist but is specifically designed for reporting scoping reviews.

It includes additional items relevant to scoping reviews, such as charting methods, stakeholder consultation, and the presentation of a broader range of evidence sources beyond empirical studies.

References:

Arksey, H., & O’Malley, L. (2005). Scoping studies: towards a methodological framework. International Journal of Social Research Methodology, 8 (1), 19-32.

Centre for Reviews and Dissemination (CRD). (2001). Undertaking systematic reviews of research on effectiveness: CRD’s guidance for those carrying out or commissioning reviews. York: University of York.

Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors).  Cochrane Handbook for Systematic Reviews of Interventions  version 6.4 (updated August 2023). Cochrane, 2023. Available from www.training.cochrane.org/handbook.

Levac, D., Colquhoun, H., & O’Brien, K. K. (2010). Scoping studies: advancing the methodology. Implementation Science, 5 (1), 69.

Munn, Z., Pollock, D., Khalil, H., Alexander, L., Mclnerney, P., Godfrey, C. M., … & Tricco, A. C. (2022). What are scoping reviews? Providing a formal definition of scoping reviews as a type of evidence synthesis .  JBI evidence synthesis ,  20 (4), 950-952.

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What is a Literature Review?

Description.

A literature review, also called a review article or review of literature, surveys the existing research on a topic. The term "literature" in this context refers to published research or scholarship in a particular discipline, rather than "fiction" (like American Literature) or an individual work of literature. In general, literature reviews are most common in the sciences and social sciences.

Literature reviews may be written as standalone works, or as part of a scholarly article or research paper. In either case, the purpose of the review is to summarize and synthesize the key scholarly work that has already been done on the topic at hand. The literature review may also include some analysis and interpretation. A literature review is  not  a summary of every piece of scholarly research on a topic.

Why are literature reviews useful?

Literature reviews can be very helpful for newer researchers or those unfamiliar with a field by synthesizing the existing research on a given topic, providing the reader with connections and relationships among previous scholarship. Reviews can also be useful to veteran researchers by identifying potentials gaps in the research or steering future research questions toward unexplored areas. If a literature review is part of a scholarly article, it should include an explanation of how the current article adds to the conversation. (From: https://library.drake.edu/englit/criticism)

How is a literature review different from a research article?

Research articles: "are empirical articles that describe one or several related studies on a specific, quantitative, testable research question....they are typically organized into four text sections: Introduction, Methods, Results, Discussion." Source: https://psych.uw.edu/storage/writing_center/litrev.pdf)

Steps for Writing a Literature Review

1. Identify and define the topic that you will be reviewing.

The topic, which is commonly a research question (or problem) of some kind, needs to be identified and defined as clearly as possible.  You need to have an idea of what you will be reviewing in order to effectively search for references and to write a coherent summary of the research on it.  At this stage it can be helpful to write down a description of the research question, area, or topic that you will be reviewing, as well as to identify any keywords that you will be using to search for relevant research.

2. Conduct a Literature Search

Use a range of keywords to search databases such as PsycINFO and any others that may contain relevant articles.  You should focus on peer-reviewed, scholarly articles . In SuperSearch and most databases, you may find it helpful to select the Advanced Search mode and include "literature review" or "review of the literature" in addition to your other search terms.  Published books may also be helpful, but keep in mind that peer-reviewed articles are widely considered to be the “gold standard” of scientific research.  Read through titles and abstracts, select and obtain articles (that is, download, copy, or print them out), and save your searches as needed. Most of the databases you will need are linked to from the Cowles Library Psychology Research guide .

3. Read through the research that you have found and take notes.

Absorb as much information as you can.  Read through the articles and books that you have found, and as you do, take notes.  The notes should include anything that will be helpful in advancing your own thinking about the topic and in helping you write the literature review (such as key points, ideas, or even page numbers that index key information).  Some references may turn out to be more helpful than others; you may notice patterns or striking contrasts between different sources; and some sources may refer to yet other sources of potential interest.  This is often the most time-consuming part of the review process.  However, it is also where you get to learn about the topic in great detail. You may want to use a Citation Manager to help you keep track of the citations you have found. 

4. Organize your notes and thoughts; create an outline.

At this stage, you are close to writing the review itself.  However, it is often helpful to first reflect on all the reading that you have done.  What patterns stand out?  Do the different sources converge on a consensus?  Or not?  What unresolved questions still remain?  You should look over your notes (it may also be helpful to reorganize them), and as you do, to think about how you will present this research in your literature review.  Are you going to summarize or critically evaluate?  Are you going to use a chronological or other type of organizational structure?  It can also be helpful to create an outline of how your literature review will be structured.

5. Write the literature review itself and edit and revise as needed.

The final stage involves writing.  When writing, keep in mind that literature reviews are generally characterized by a  summary style  in which prior research is described sufficiently to explain critical findings but does not include a high level of detail (if readers want to learn about all the specific details of a study, then they can look up the references that you cite and read the original articles themselves).  However, the degree of emphasis that is given to individual studies may vary (more or less detail may be warranted depending on how critical or unique a given study was).   After you have written a first draft, you should read it carefully and then edit and revise as needed.  You may need to repeat this process more than once.  It may be helpful to have another person read through your draft(s) and provide feedback.

6. Incorporate the literature review into your research paper draft. (note: this step is only if you are using the literature review to write a research paper. Many times the literature review is an end unto itself).

After the literature review is complete, you should incorporate it into your research paper (if you are writing the review as one component of a larger paper).  Depending on the stage at which your paper is at, this may involve merging your literature review into a partially complete Introduction section, writing the rest of the paper around the literature review, or other processes.

These steps were taken from: https://psychology.ucsd.edu/undergraduate-program/undergraduate-resources/academic-writing-resources/writing-research-papers/writing-lit-review.html#6.-Incorporate-the-literature-r

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• Published: 02 July 2024

Unravelling the complexity of ventilator-associated pneumonia: a systematic methodological literature review of diagnostic criteria and definitions used in clinical research

• Markus Fally 1 ,
• Faiuna Haseeb 2 , 3 ,
• Ahmed Kouta 2 , 3 ,
• Jan Hansel 3 , 4 ,
• Rebecca C. Robey 2 , 3 ,
• Thomas Williams 5 ,
• Tobias Welte 6 ,
• Timothy Felton 2 , 3 , 5 &
• Alexander G. Mathioudakis 2 , 3  

Critical Care volume  28 , Article number:  214 ( 2024 ) Cite this article

2833 Accesses

60 Altmetric

Metrics details

Ventilator-associated pneumonia (VAP) is a prevalent and grave hospital-acquired infection that affects mechanically ventilated patients. Diverse diagnostic criteria can significantly affect VAP research by complicating the identification and management of the condition, which may also impact clinical management.

We conducted this review to assess the diagnostic criteria and the definitions of the term “ventilator-associated” used in randomised controlled trials (RCTs) of VAP management.

Search methods

Based on the protocol (PROSPERO 2019 CRD42019147411), we conducted a systematic search on MEDLINE/PubMed and Cochrane CENTRAL for RCTs, published or registered between 2010 and 2024.

Selection criteria

We included completed and ongoing RCTs that assessed pharmacological or non-pharmacological interventions in adults with VAP.

Data collection and synthesis

Data were collected using a tested extraction sheet, as endorsed by the Cochrane Collaboration. After cross-checking, data were summarised in a narrative and tabular form.

In total, 7,173 records were identified through the literature search. Following the exclusion of records that did not meet the eligibility criteria, 119 studies were included. Diagnostic criteria were provided in 51.2% of studies, and the term “ventilator-associated” was defined in 52.1% of studies. The most frequently included diagnostic criteria were pulmonary infiltrates (96.7%), fever (86.9%), hypothermia (49.1%), sputum (70.5%), and hypoxia (32.8%). The different criteria were used in 38 combinations across studies. The term “ventilator-associated” was defined in nine different ways.

Conclusions

When provided, diagnostic criteria and definitions of VAP in RCTs display notable variability. Continuous efforts to harmonise VAP diagnostic criteria in future clinical trials are crucial to improve quality of care, enable accurate epidemiological assessments, and guide effective antimicrobial stewardship.

Ventilator-associated pneumonia (VAP) stands as the most prevalent and serious hospital-acquired infection observed in intensive care units [ 1 ]. VAP prolongs hospital stays, durations of mechanical ventilation, and is associated with considerable mortality and an increase in healthcare costs [ 2 , 3 ].

Diagnosing VAP can be challenging for clinicians as it shares clinical signs and symptoms with other forms of pneumonia as well as non-infectious conditions [ 4 ]. The most recent international clinical guidelines define VAP as the presence of respiratory infection signs combined with new radiographic infiltrates in a patient who has been ventilated for at least 48 h [ 5 , 6 ]. While the guidelines developed by ERS/ESICM/ESCMID/ALAT do not provide a detailed definition of signs of respiratory infection [ 5 ], the ATS/IDSA guidelines mention that clinical signs may include the new onset of fever, purulent sputum, leucocytosis, and decline in oxygenation [ 6 ]. However, the ATS/IDSA guideline panel also acknowledges that there is no gold standard for the diagnosis of VAP [ 6 ]. This lack of a standardised definition is further highlighted by the varying, surveillance-based definitions of VAP provided by the Centre for Disease Control (CDC) and the European Centre for Disease Control (ECDC) [ 7 , 8 ]. These definitions, focusing on a combination of clinical, radiological, and microbiological signs to identify cases of VAP, were established to standardise reporting and facilitate the monitoring of infections in healthcare settings. However, the criteria given by the CDC and ECDC may not always align with the diagnostic criteria used by clinicians to confirm or rule out the condition [ 9 , 10 , 11 ].

Variations in the eligibility criteria applied to VAP can have a significant impact on systematic reviews and meta-analyses that assess different interventions, primarily due to the potential lack of comparability among the studied populations [ 12 ]. Furthermore, the incidence of VAP may be underestimated when excessively strict diagnostic criteria are employed [ 13 , 14 ].

A recent systematic review conducted by Weiss et al. focused on inclusion and judgment criteria used in randomised controlled trials (RCTs) on nosocomial pneumonia and found considerable heterogeneity [ 15 ]. However, the authors only considered RCTs evaluating antimicrobial treatment as interventions, did not distinguish between hospital-acquired pneumonia (HAP) and VAP, and did not evaluate definitions of the term "ventilator-associated".

The objective of this systematic review was to provide a concise overview of the diagnostic criteria for VAP recently used in RCTs, as well as the definitions attributed to the term "ventilator-associated". Its findings will provide valuable insights to a forthcoming task force, which aims to establish a uniform definition and diagnostic criteria for VAP in clinical trials. The task force will be made up of representatives from prominent international societies with an interest in VAP, as well as patient partners with lived experience. The harmonisation of the diagnostic criteria for VAP in upcoming clinical research are vital for enhancing patient care, enabling accurate epidemiological studies, and guiding successful antimicrobial stewardship programs.

Protocol and registration

The protocol for this systematic review was registered in advance with the International Prospective Register of Systematic Reviews (PROSPERO 2019 CRD42019147411), encompassing a broad review focusing on pneumonia outcomes and diagnostic criteria in RCTs. Recognising the limitations of discussing all findings in one manuscript, we opted to produce several focused and comprehensive manuscripts, all employing the same fundamental methodology, as registered with PROSPERO. While a previous publication focused on outcomes reported in RCTs on pneumonia management [ 16 ], the current submission specifically addresses diagnostic criteria for VAP.

Eligibility criteria

We included RCTs that were registered, planned, and/or completed that: (1) enrolled adults with VAP; and (2) assessed the safety, efficacy and/or effectiveness of pharmacological or non-pharmacological interventions for treating VAP.

We have excluded systematic reviews, meta-analyses, narrative reviews, post hoc analyses from RCTs, observational studies, case reports, editorials, conference proceedings, and studies that do not exclusively focus on pneumonia (such as trials including patients with pneumonia alongside other diseases). Additionally, studies on pneumonia subtypes other than VAP, such as pneumonia without specifying a subtype, community-acquired pneumonia (CAP), healthcare-associated pneumonia (HCAP), and HAP, have also been excluded. To maintain focus and relevance, studies on Coronavirus Disease 2019 (COVID-19) were excluded from this systematic review, as the viral aetiology and distinct clinical management protocols differ significantly from the nature and treatment strategies of VAP. RCT protocols were only included if the results have not been previously published in another article included in this systematic review. Due to resource constraints and the lack of multilingual expertise within the review team, this systematic review was restricted to English-language RCTs.

Information sources and search

On 20 May 2024, we searched MEDLINE/PubMed, and the Cochrane Register of Controlled Trials (CENTRAL) for RCTs published between 1 January 2010 and 19 May 2024. We used electronic algorithms introducing a combination of controlled vocabulary and search terms as reported in the Appendix.

Study selection

Two reviewers (FH, MF) independently screened titles and abstracts to identify eligible studies using Rayyan [ 17 ]. In case of disagreement, a third reviewer was consulted (AGM). After immediate exclusion of duplicates using EndNote X9, four reviewers (AGM, FH, JH, MF) independently checked for eligibility at full-text level. The results of the selection process are reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [ 18 ].

Data collection process

We developed an extraction sheet as endorsed by the Cochrane Collaboration [ 19 ]. The extraction sheet was independently tested by three reviewers (AGM, FH, MF) on five randomly selected studies and adapted to ensure good inter-reviewer agreement. The extraction sheet contained the following elements: (1) study ID, name, reference and NCT number; (2) type of pneumonia: CAP, HCAP, HAP and/or VAP; (3) diagnostic criteria for pneumonia; (4) definition of setting; (5) study origin, design, populations, interventions, and outcomes.

Four reviewers (AGM, FH, JH, MF) extracted data from the eligible studies. Data were extracted sequentially from either a manuscript containing published results, a published protocol, or, upon obtaining a trial registration number from CENTRAL, from one of the designated trial registries, such as ClinicalTrials.gov, the Clinical Trials Registry India (CTRI), the Chinese Clinical Trial Registry (ChiCTR), the European Clinical Trials Database (EudraCT), the Iranian Registry of Clinical Trials (IRCT), the Japan Primary Registries Network (JPRN), and the Japanese University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR). Cross-checking of all extracted data was performed by a second reviewer (AGM, AK, MF, RR, TW). Disagreements regarding data collection were resolved by discussion between all reviewers.

Synthesis of results

The findings were consolidated through a combination of narrative and tabular formats. The presentation encompassed the quantitative representation of each diagnostic criterion in terms of numerical values and proportions. Additionally, we provide an analysis of the various combinations of diagnostic criteria employed in RCTs in a sunburst diagram and a tabular format, along with an examination of the definitions attributed to the term "ventilator-associated".

Risk of bias

The main goal of this systematic review was to explore the diagnostic criteria used in clinical trials for diagnosing VAP. It covered trials with published protocols and/or results, as well as those only registered in a trial database. The varying levels and gaps in the information provided by the various sources made it difficult to conduct a reliable and meaningful risk of bias assessment for all included studies. However, for RCTs with published data, risk of bias was evaluated by four reviewers (AGM, JH, MF, RR) using the Risk of Bias in Randomized Trials 2 tool (RoB-2 tool), as endorsed by the Cochrane Collaboration [ 20 ].

Study selection and characteristics

A total of 7173 records were identified through the databases MEDLINE and CENTRAL, as illustrated in Fig.  1 . Following the removal of duplicate entries, a screening process involving the evaluation of titles and abstracts was conducted on 5652 records. Among these, 650 records were deemed potentially eligible for inclusion. Ultimately, our review included 119 studies that specifically focused on VAP (Table S1 in the Appendix, the full dataset is available online [ 21 ]).

PRISMA flowchart showing study selection

The total number of patients in the 119 identified studies was 21,289. Among these studies, 83 focused exclusively on VAP, while the remaining studies encompassed various subtypes of pneumonia in addition to VAP (see Table  1 ). The majority of these studies were registered, and their protocols were accessible either through publication in a journal article or on a clinical trial platform. Results were accessible in 56.3% of cases, while both results and the protocol were accessible in 36.9% of cases. In 40.3% of the included studies, data could only be obtained from a trial registry platform, with ClinicalTrials.gov being the primary platform in 36 out of 48 cases, and ChiCTR (n = 2), CTRI (n = 3), EudraCT (n = 3), IRCT (n = 2), JPRN (n = 1) and UMIN-CTR (n = 1) in the remaining cases.

Diagnostic criteria were provided in 51.2% and the term “ventilator-associated” was defined in 52.1% of the studies, respectively. Of the 20 studies (16.8%) that referred to previously published diagnostic criteria, 13 cited the Clinical Pulmonary Infection Score (CPIS) [ 22 ], while the remaining referred to national and international guidelines.

We evaluated the risk of bias in 67 studies with published results using the RoB-2 tool. The overall assessment showed that 25% of the studies were at high risk of bias, 30% were at low risk of bias, and the remaining 45% had some concerns about potential bias. These results indicate variability in the methodological quality of the studies included in the review. The overall risk of bias and the detailed results of our assessments for the 67 studies are displayed in the Appendix (Figures SF1-SF2).

Diagnostic criteria for VAP

Pulmonary infiltrates.

Of the 61 studies on VAP that provided diagnostic criteria, 59 (96.7%) included the radiological evidence of a new or progressive pulmonary infiltrate.

Clinical signs and symptoms

The most frequently included clinical signs and symptoms were fever (86.9%), hypothermia (49.1%), sputum (70.5%), and hypoxia (32.8%). Different cut-off values were employed to define fever and hypothermia, as indicated in Table  2 . The majority of studies, accounting for 45.2%, utilised a cut-off of > 38 degrees Celsius (°C) to define fever, while 13.2% of studies used a cut-off of ≥ 38°C. In the case of hypothermia, the most commonly employed cut-off value was < 35°C, which was utilised in 43.3% of studies that included hypothermia as a criterion. Only a minority of studies provided information on the site of temperature measurement. Oral measurement was the most frequently employed method, followed by axillary and core temperature measurements (further details are displayed in Table S2 in the Appendix).

Biochemistry criteria

Fifty-four studies (88.5%) incorporated white blood count abnormalities as part of their diagnostic criteria for VAP. Conversely, only one study included an elevation of procalcitonin (PCT) as a diagnostic factor, and none of the identified studies included C-reactive protein (CRP). The specific thresholds for leucocytosis and leucopoenia varied across studies, with leucocyte counts ranging from greater than 10,000/mm3 to greater than 12,000/mm3 for leucocytosis, and less than 3,500/mm3 to less than 4,500/mm3 for leucopoenia (Table  3 ).

Combinations of diagnostic criteria

All definitions of pneumonia were composite in nature and required the fulfilment of a minimum number of predetermined criteria for the diagnosis to be established. In 90.2% of the studies the presence of a new pulmonary infiltrate was a mandatory criterion. Two studies did not include an infiltrate as criterion, whereas the remaining studies (n = 4) included the presence of an infiltrate in their criteria, it was, however, not required for a diagnosis.

The most commonly employed set of diagnostic criteria (18/61, 29.5%) consisted of a pulmonary infiltrate along with two or more additional criteria. However, these additional criteria varied across studies (Fig.  2 ). A quarter (17/61) of the included studies that provided diagnostic criteria required the fulfilment of all individual criteria for diagnosis, including an infiltrate. An infiltrate and one or more additional criteria were used to establish a diagnosis of VAP in 14.8% of studies (9/61). A total of 38 different combinations of diagnostic criteria for VAP were used in the 61 identified studies. A full set of these criteria is displayed in Table S3 in the Appendix.

The different combinations of diagnostic criteria used in VAP RCTs. CXR radiological evidence of a new infiltrate; T temperature criterion; WBC white blood count criterion; dys/tach dyspnoea and/or tachypnoea; O2 hypoxia; auscultation  auscultation abnormalities

Definition of “ventilator-associated”

We noted that 52.1% of included studies incorporated a specific definition of the term “ventilator-associated” (Table  4 ). A total of nine distinct definitions were identified across 62 RCTs. The definition most commonly used was “onset after > 48 h of mechanical ventilation” (82.3%). Other definitions employed varying time thresholds, ranging from 24 h to seven days. Additionally, certain studies introduced supplementary criteria to further delineate the concept of “ventilator-associated”, such as administration of antibiotics prior to mechanical ventilation, duration of hospitalisation, or the timing of extubation.

Summary of evidence

This systematic review provides a concise overview of the diagnostic criteria for VAP used in RCTs and the definitions attributed to the term “ventilator-associated”. A total of 119 studies on VAP, published or registered between 2010 and 2024, were included, spanning a total of 21,289 patients. The majority of studies focused exclusively on VAP, while some also included other subtypes of pneumonia alongside VAP. Diagnostic criteria were provided in only 51.2% of the studies, and the term “ventilator-associated” was defined in only 52.1% of the studies. The most commonly utilised definition for “ventilator-associated” was “onset after > 48 h of mechanical ventilation”, used by 82.3% of studies providing a definition.

In clinical practice, the diagnosis of VAP is often based on a combination of clinical signs, laboratory results, and imaging findings, yet these are not without their limitations [ 8 ]. Our systematic review revealed considerable heterogeneity among diagnostic criteria for VAP in recent RCTs. Various combinations of specific criteria were employed to define VAP, leading to significant variability. Moreover, commonly used criteria were defined in different ways, with variations observed in the thresholds set for fever/hypothermia, as well as leucocytosis/leucopoenia.

Several criteria that were used in the studies included in our review have been shown to be insufficient for confirming a diagnosis of VAP. One of the most important criteria, included in the majority of reviewed RCTs, a new or progressive pulmonary infiltrate, has previously been reported to be of limited diagnostic value due to a lack of specificity [ 14 ]. Additionally, criteria like fever/hypothermia and the measurement of biomarkers such as leukocytes, CRP, and PCT may not be effective in diagnosing or excluding VAP in various clinical settings [ 4 , 23 , 24 ]. Despite this, CRP is widely used and has demonstrated some clinical value in predicting VAP [ 25 ]. It is, therefore, surprising that none of the RCTs included in our review employed CRP as a diagnostic criterion.

Overall, the findings of our systematic review underline the diverse nature of VAP, with different diagnostic criteria increasing the risk of both over- and underdiagnosis of VAP [ 14 , 26 ]. There have been attempts to diagnose VAP more objectively, one of these being the development of the CPIS in 1991, a six-component score that 10.9% of studies included in our review referred to [ 27 ]. This score includes different cut-offs for body temperature, leucocyte counts, tracheal secretion appearances, oxygenation levels and radiographical changes to estimate the risk for VAP. However, the CPIS has been shown not to be superior to other diagnostic criteria, and, therefore, its application remains controversial [ 8 , 11 , 22 , 28 ]. Other commonly applied criteria, such as the surveillance-based criteria by the ECDC and CDC, did not seem to be accurate enough to detect true cases of VAP either [ 9 , 10 , 11 ]. Furthermore, there is limited agreement between the two surveillance-based criteria, which has previously resulted in different estimates of VAP events [ 29 ].

In lieu of definitive diagnostic scores or sets of diagnostic criteria to detect all true cases of VAP, the findings of our systematic review indicate the need for more homogeneous diagnostic criteria in future RCTs, to assure their comparability. Currently, international guidelines avoid providing clear diagnostic criteria for VAP [ 5 , 6 ]. Given the significance of establishing strong consensus definitions for high-risk conditions like VAP, it is essential to emphasise even further that a uniform definition is crucial not only for advancing therapeutic research but also, and perhaps more importantly, for refining diagnostic methods. Together with core outcome sets, these definitions can help to improve the likelihood of attaining robust and reliable findings in forthcoming systematic reviews and meta-analyses [ 16 , 30 ].

Strengths and limitations

We used a comprehensive search strategy which included multiple databases and a wide range of search terms, ensuring broad identification of all potentially relevant trials. Additionally, the inclusion criteria were clearly defined, and the study selection process was conducted independently by multiple reviewers to minimise bias. The extraction sheet used for data collection was tested for inter-reviewer agreement and adapted accordingly. Another strength is the open availability of the complete dataset, maximising the transparency and reproducibility of our findings.

However, the following limitations need to be acknowledged. Firstly, the review only included RCTs conducted in English, which may have introduced language bias. This approach was adopted to ensure feasible and reliable data analysis within the scope of the resources available.

Additionally, the exclusion of studies focusing on pneumonia subtypes other than VAP may limit the generalisability of our findings. Furthermore, the lack of diagnostic criteria and definitions in a significant proportion of included studies suggests a potential reporting bias. This might be reinforced by the fact that 40.3% of data were received from trial registry platforms. Compared to final manuscript publications, reporting of eligibility criteria is often incomplete on registry platforms, therefore this must be highlighted as a limitation [ 31 ].

This systematic review provides an overview of diagnostic criteria for VAP used in RCTs and the definitions attributed to the term “ventilator-associated”. Our findings highlight the heterogeneity and lack of standardisation in commonly used diagnostic criteria, as well as the variability in definitions of "ventilator-associated" across clinical trials. We emphasise the need for a uniform definition of VAP to enable better comparability between studies and interventions. The results of this review will inform the work of an upcoming task force aimed at establishing such standardised criteria.

Availability of data and materials

Raw data are accessible via the Open Science Framework (OSF) at osf.io/v3 × 42. This link is referenced in our manuscript (Ref. 21).

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Acknowledgements

We would like to acknowledge and honour the contributions of Prof. Tobias Welte, who was a vital member of our research team and co-author of this manuscript. Prof. Welte passed away after the initial submission of this work but before its final acceptance. His insights and expertise were invaluable to the development of this research, and he remains deeply missed by the team. We dedicate this work to his memory.

Open access funding provided by Copenhagen University This study was partly supported by the NIHR Manchester Biomedical Research Centre (BRC, NIHR203308) as well as the Capital Region of Denmark (Region Hovedstaden). The funders had no role in study design, data collection or analysis, decision to publish, nor preparation of the manuscript. Dr Jan Hansel was supported by an NIHR Academic Clinical Fellowship in Intensive Care Medicine. Dr Rebecca Robey was supported by an NIHR Academic Clinical Fellowship in Respiratory Medicine. Dr Alexander G. Mathioudakis was supported by an NIHR Clinical Lectureship in Respiratory Medicine. All authors have completed a ICMJE uniform disclosure form detailing any conflicts of interest outside the submitted work that they may have. None of the authors have conflicts directly related to this work.

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Markus Fally

North West Lung Centre, Wythenshawe Hospital, Manchester University NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK

Faiuna Haseeb, Ahmed Kouta, Rebecca C. Robey, Timothy Felton & Alexander G. Mathioudakis

Division of Immunology, Immunity to Infection and Respiratory Medicine, School of Biological Sciences, The University of Manchester, Manchester, UK

Faiuna Haseeb, Ahmed Kouta, Jan Hansel, Rebecca C. Robey, Timothy Felton & Alexander G. Mathioudakis

North West School of Intensive Care Medicine, Health Education England North West, Manchester, UK

Acute Intensive Care Unit, Wythenshawe Hospital, Manchester University NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK

Thomas Williams & Timothy Felton

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MF: conceptualisation, methodology, software, formal analysis, investigation, data curation, writing—original draft, visualisation, project administration. FH: conceptualisation, investigation, data curation, validation, writing—review and editing. AK, JH, RCR and TWI: data curation, validation, writing—review and editing. TWE: conceptualisation, investigation, methodology, resources, validation, writing—review and editing. TF: conceptualisation, investigation, methodology, resources, validation, writing—review and editing, supervision. AGM: conceptualisation, investigation, methodology, software, resources, validation, writing—review and editing, project administration, supervision, funding acquisition, project administration.

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Additional file1 (docx 807 kb), search strategy, medline/pubmed.

#1: pneumonia [mh]

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Fally, M., Haseeb, F., Kouta, A. et al. Unravelling the complexity of ventilator-associated pneumonia: a systematic methodological literature review of diagnostic criteria and definitions used in clinical research. Crit Care 28 , 214 (2024). https://doi.org/10.1186/s13054-024-04991-3

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DOI : https://doi.org/10.1186/s13054-024-04991-3

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Comparative cardioprotective effectiveness: noacs vs. nattokinase—bridging basic research to clinical findings.

1. Introduction

2. the role of noacs in coagulation cascade, 2.1. inhibition of fxa as a therapeutic strategy, 2.2. thrombin inhibition as a therapeutic strategy, 3. noacs through the scope of large clinical trials, 4. nattokinase—a promising agent for cvd treatment, 5. cardioprotection beyond anticoagulation—evidence from basic and clinical research, 5.1. effects on myocardial structure and function, 5.2. antihypertensive effects, 5.3. antifibrotic and antihypertrophic effects, 5.4. anti-inflammatory, anti-atherosclerotic effects and effects on vasculature and endothelial function, 5.5. antioxidative effects, 5.6. anti-apoptotic effects, 6. concluding remarks and future directions, author contributions, acknowledgments, conflicts of interest.

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Muric, M.; Nikolic, M.; Todorovic, A.; Jakovljevic, V.; Vucicevic, K. Comparative Cardioprotective Effectiveness: NOACs vs. Nattokinase—Bridging Basic Research to Clinical Findings. Biomolecules 2024 , 14 , 956. https://doi.org/10.3390/biom14080956

Muric M, Nikolic M, Todorovic A, Jakovljevic V, Vucicevic K. Comparative Cardioprotective Effectiveness: NOACs vs. Nattokinase—Bridging Basic Research to Clinical Findings. Biomolecules . 2024; 14(8):956. https://doi.org/10.3390/biom14080956

Muric, Maja, Marina Nikolic, Andreja Todorovic, Vladimir Jakovljevic, and Ksenija Vucicevic. 2024. "Comparative Cardioprotective Effectiveness: NOACs vs. Nattokinase—Bridging Basic Research to Clinical Findings" Biomolecules 14, no. 8: 956. https://doi.org/10.3390/biom14080956

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