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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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Systematic Reviews

Describes what is involved with conducting a systematic review of the literature for evidence-based public health and how the librarian is a partner in the process.

Several CDC librarians have special training in conducting literature searches for systematic reviews.  Literature searches for systematic reviews can take a few weeks to several months from planning to delivery.

Fill out a search request form here  or contact the Stephen B. Thacker CDC Library by email  [email protected] or telephone 404-639-1717.

Campbell Collaboration

Cochrane Collaboration

Eppi Centre

Joanna Briggs Institute

McMaster University

PRISMA Statement

Systematic Reviews – CRD’s Guide

Systematic Reviews of Health Promotion and Public Health Interventions

The Guide to Community Preventive Services

Look for systematic reviews that have already been published. 

• To ensure that the work has not already been done.
• To provides examples of search strategies for your topic

Look in PROSPERO for registered systematic reviews.

Search Cochrane and CRD-York for systematic reviews.

Search filter for finding systematic reviews in PubMed

Other search filters to locate systematic reviews

A systematic review attempts to collect and analyze all evidence that answers a specific question.  The question must be clearly defined and have inclusion and exclusion criteria. A broad and thorough search of the literature is performed and a critical analysis of the search results is reported and ultimately provides a current evidence-based answer  to the specific question.

Time:  According to Cochrane , it takes 18 months on average to complete a Systematic Review.

The average systematic review from beginning to end requires 18 months of work. “…to find out about a healthcare intervention it is worth searching research literature thoroughly to see if the answer is already known. This may require considerable work over many months…” ( Cochrane Collaboration )

Review Team: Team Members at minimum…

• Content expert
• 2 reviewers
• 1 tie breaker
• 1 statistician (meta-analysis)
• 1 economist if conducting an economic analysis
• *1 librarian (expert searcher) trained in systematic reviews

“Expert searchers are an important part of the systematic review team, crucial throughout the review process-from the development of the proposal and research question to publication.” ( McGowan & Sampson, 2005 )

*Ask your librarian to write a methods section regarding the search methods and to give them co-authorship. You may also want to consider providing a copy of one or all of the search strategies used in an appendix.

The Question to Be Answered: A clearly defined and specific question or questions with inclusion and exclusion criteria.

Written Protocol: Outline the study method, rationale, key questions, inclusion and exclusion criteria, literature searches, data abstraction and data management, analysis of quality of the individual studies, synthesis of data, and grading of the evidience for each key question.

Literature Searches:  Search for any systematic reviews that may already answer the key question(s).  Next, choose appropriate databases and conduct very broad, comprehensive searches.  Search strategies must be documented so that they can be duplicated.  The librarian is integral to this step of the process. Before your librarian creates a search strategy and starts searching in earnest you should write a detailed PICO question , determine the inclusion and exclusion criteria for your study, run a preliminary search, and have 2-4 articles that already fit the criteria for your review.

What is searched depends on the topic of the review but should include…

• At least 3 standard medical databases like PubMed/Medline, CINAHL, Embase, etc..
• At least 2 grey literature resources like Clinicaltrials.gov, COS Conference Papers Index, Grey Literature Report,  etc…

Citation Management: EndNote is a bibliographic management tools that assist researchers in managing citations.  The Stephen B. Thacker CDC Library oversees the site license for EndNote.

To request installation:   The library provides EndNote  to CDC staff under a site-wide license. Please use the ITSO Software Request Tool (SRT) and submit a request for the latest version (or upgraded version) of EndNote. Please be sure to include the computer name for the workstation where you would like to have the software installed.

EndNote Training:   CDC Library offers training on EndNote on a regular basis – both a basic and advanced course. To view the course descriptions and upcoming training dates, please visit the CDC Library training page .

For assistance with EndNote software, please contact [email protected]

Vendor Support and Services:   EndNote – Support and Services (Thomson Reuters)  EndNote – Tutorials and Live Online Classes (Thomson Reuters)

Getting Articles:

Articles can be obtained using DocExpress or by searching the electronic journals at the Stephen B. Thacker CDC Library.

IOM Standards for Systematic Reviews: Standard 3.1: Conduct a comprehensive systematic search for evidence

The goal of a systematic review search is to maximize recall and precision while keeping results manageable. Recall (sensitivity) is defined as the number of relevant reports identified divided by the total number of relevant reports in existence. Precision (specificity) is defined as the number of relevant reports identified divided by the total number of reports identified.

Issues to consider when creating a systematic review search:   

• All concepts are included in the strategy
• All appropriate subject headings are used
• Appropriate use of explosion
• Appropriate use of subheadings and floating subheadings
• Use of natural language (text words) in addition to controlled vocabulary terms
• Use of appropriate synonyms, acronyms, etc.
• Truncation and spelling variation as appropriate
• Appropriate use of limits such as language, years, etc.
• Field searching, publication type, author, etc.
• Boolean operators used appropriately
• Line errors: when searches are combined using line numbers, be sure the numbers refer to the searches intended
• Check indexing of relevant articles
• Search strategy adapted as needed for multiple databases
• Cochrane Handbook: Searching for Studies See Part 2, Chapter 6

A step-by-step guide to systematically identify all relevant animal studies

Materials listed in these guides are selected to provide awareness of quality public health literature and resources. A material’s inclusion does not necessarily represent the views of the U.S. Department of Health and Human Services (HHS), the Public Health Service (PHS), or the Centers for Disease Control and Prevention (CDC), nor does it imply endorsement of the material’s methods or findings. HHS, PHS, and CDC assume no responsibility for the factual accuracy of the items presented. The selection, omission, or content of items does not imply any endorsement or other position taken by HHS, PHS, and CDC. Opinion, findings, and conclusions expressed by the original authors of items included in these materials, or persons quoted therein, are strictly their own and are in no way meant to represent the opinion or views of HHS, PHS, or CDC. References to publications, news sources, and non-CDC Websites are provided solely for informational purposes and do not imply endorsement by HHS, PHS, or CDC.

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Library Services

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• Guides and databases
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• Systematic reviews

What are systematic reviews?

• Types of systematic reviews
• Formulating a research question
• Identifying studies
• Searching databases
• Describing and appraising studies
• Synthesis and systematic maps
• Software for systematic reviews
• Online training and support
• Live and face to face training
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• Further help

Systematic reviews are a type of literature review of research which require equivalent standards of rigour as primary research. They have a clear, logical rationale that is reported to the reader of the review. They are used in research and policymaking to inform evidence-based decisions and practice. They differ from traditional literature reviews particularly in the following elements of conduct and reporting.

Systematic reviews: 

• use explicit and transparent methods
• are a piece of research following a standard set of stages
• are accountable, replicable and updateable
• involve users to ensure a review is relevant and useful.

For example, systematic reviews (like all research) should have a clear research question, and the perspective of the authors in their approach to addressing the question is described. There are clearly described methods on how each study in a review was identified, how that study was appraised for quality and relevance and how it is combined with other studies in order to address the review question. A systematic review usually involves more than one person in order to increase the objectivity and trustworthiness of the reviews methods and findings.

Research protocols for systematic reviews may be peer-reviewed and published or registered in a suitable repository to help avoid duplication of reviews and for comparisons to be made with the final review and the planned review.

• History of systematic reviews to inform policy (EPPI-Centre)
• Six reasons why it is important to be systematic (EPPI-Centre)
• Evidence Synthesis International (ESI): Position Statement Describes the issues, principles and goals in synthesising research evidence to inform policy, practice and decisions

On this page

Should all literature reviews be 'systematic reviews', different methods for systematic reviews, reporting standards for systematic reviews.

Literature reviews provide a more complete picture of research knowledge than is possible from individual pieces of research. This can be used to: clarify what is known from research, provide new perspectives, build theory, test theory, identify research gaps or inform research agendas.

A systematic review requires a considerable amount of time and resources, and is one type of literature review.

If the purpose of a review is to make justifiable evidence claims, then it should be systematic, as a systematic review uses rigorous explicit methods. The methods used can depend on the purpose of the review, and the time and resources available.

A 'non-systematic review' might use some of the same methods as systematic reviews, such as systematic approaches to identify studies or quality appraise the literature. There may be times when this approach can be useful. In a student dissertation, for example, there may not be the time to be fully systematic in a review of the literature if this is only one small part of the thesis. In other types of research, there may also be a need to obtain a quick and not necessarily thorough overview of a literature to inform some other work (including a systematic review). Another example, is where policymakers, or other people using research findings, want to make quick decisions and there is no systematic review available to help them. They have a choice of gaining a rapid overview of the research literature or not having any research evidence to help their decision-making. 

Just like any other piece of research, the methods used to undertake any literature review should be carefully planned to justify the conclusions made. 

Finding out about different types of systematic reviews and the methods used for systematic reviews, and reading both systematic and other types of review will help to understand some of the differences. 

Typically, a systematic review addresses a focussed, structured research question in order to inform understanding and decisions on an area. (see the  Formulating a research question  section for examples). 

Sometimes systematic reviews ask a broad research question, and one strategy to achieve this is the use of several focussed sub-questions each addressed by sub-components of the review.  

Another strategy is to develop a map to describe the type of research that has been undertaken in relation to a research question. Some maps even describe over 2,000 papers, while others are much smaller. One purpose of a map is to help choose a sub-set of studies to explore more fully in a synthesis. There are also other purposes of maps: see the box on  systematic evidence maps  for further information. 

Reporting standards specify minimum elements that need to go into the reporting of a review. The reporting standards refer mainly to methodological issues but they are not as detailed or specific as critical appraisal for the methodological standards of conduct of a review.

A number of organisations have developed specific guidelines and standards for both the conducting and reporting on systematic reviews in different topic areas.  

• PRISMA PRISMA is a reporting standard and is an acronym for Preferred Reporting Items for Systematic Reviews and Meta-Analyses. The Key Documents section of the PRISMA website links to a checklist, flow diagram and explanatory notes. PRISMA is less useful for certain types of reviews, including those that are iterative.
• eMERGe eMERGe is a reporting standard that has been developed for meta-ethnographies, a qualitative synthesis method.
• ROSES: RepOrting standards for Systematic Evidence Syntheses Reporting standards, including forms and flow diagram, designed specifically for systematic reviews and maps in the field of conservation and environmental management.

Useful books about systematic reviews

Systematic approaches to a successful literature review

An introduction to systematic reviews

Cochrane handbook for systematic reviews of interventions

Systematic reviews: crd's guidance for undertaking reviews in health care.

Finding what works in health care: Standards for systematic reviews

Systematic Reviews in the Social Sciences

Meta-analysis and research synthesis.

Research Synthesis and Meta-Analysis

Doing a Systematic Review

Literature reviews.

• What is a literature review?
• Why are literature reviews important?
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• Last Updated: May 30, 2024 4:38 PM
• URL: https://library-guides.ucl.ac.uk/systematic-reviews

University Libraries      University of Nevada, Reno

• Skill Guides
• Subject Guides

Systematic, Scoping, and Other Literature Reviews: Overview

• Project Planning

What Is a Systematic Review?

Regular literature reviews are simply summaries of the literature on a particular topic. A systematic review, however, is a comprehensive literature review conducted to answer a specific research question. Authors of a systematic review aim to find, code, appraise, and synthesize all of the previous research on their question in an unbiased and well-documented manner. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) outline the minimum amount of information that needs to be reported at the conclusion of a systematic review project. 

Other types of what are known as "evidence syntheses," such as scoping, rapid, and integrative reviews, have varying methodologies. While systematic reviews originated with and continue to be a popular publication type in medicine and other health sciences fields, more and more researchers in other disciplines are choosing to conduct evidence syntheses. 

This guide will walk you through the major steps of a systematic review and point you to key resources including Covidence, a systematic review project management tool. For help with systematic reviews and other major literature review projects, please send us an email at  [email protected] .

Getting Help with Reviews

Organization such as the Institute of Medicine recommend that you consult a librarian when conducting a systematic review. Librarians at the University of Nevada, Reno can help you:

• Understand best practices for conducting systematic reviews and other evidence syntheses in your discipline
• Choose and formulate a research question
• Decide which review type (e.g., systematic, scoping, rapid, etc.) is the best fit for your project
• Determine what to include and where to register a systematic review protocol
• Select search terms and develop a search strategy
• Identify databases and platforms to search
• Find the full text of articles and other sources
• Become familiar with free citation management (e.g., EndNote, Zotero)
• Get access to you and help using Covidence, a systematic review project management tool

Doing a Systematic Review

• Plan - This is the project planning stage. You and your team will need to develop a good research question, determine the type of review you will conduct (systematic, scoping, rapid, etc.), and establish the inclusion and exclusion criteria (e.g., you're only going to look at studies that use a certain methodology). All of this information needs to be included in your protocol. You'll also need to ensure that the project is viable - has someone already done a systematic review on this topic? Do some searches and check the various protocol registries to find out. 
• Identify - Next, a comprehensive search of the literature is undertaken to ensure all studies that meet the predetermined criteria are identified. Each research question is different, so the number and types of databases you'll search - as well as other online publication venues - will vary. Some standards and guidelines specify that certain databases (e.g., MEDLINE, EMBASE) should be searched regardless. Your subject librarian can help you select appropriate databases to search and develop search strings for each of those databases.  
• Evaluate - In this step, retrieved articles are screened and sorted using the predetermined inclusion and exclusion criteria. The risk of bias for each included study is also assessed around this time. It's best if you import search results into a citation management tool (see below) to clean up the citations and remove any duplicates. You can then use a tool like Rayyan (see below) to screen the results. You should begin by screening titles and abstracts only, and then you'll examine the full text of any remaining articles. Each study should be reviewed by a minimum of two people on the project team. 
• Collect - Each included study is coded and the quantitative or qualitative data contained in these studies is then synthesized. You'll have to either find or develop a coding strategy or form that meets your needs. 
• Explain - The synthesized results are articulated and contextualized. What do the results mean? How have they answered your research question?
• Summarize - The final report provides a complete description of the methods and results in a clear, transparent fashion. 

Adapted from

Types of reviews, systematic review.

These types of studies employ a systematic method to analyze and synthesize the results of numerous studies. "Systematic" in this case means following a strict set of steps - as outlined by entities like PRISMA and the Institute of Medicine - so as to make the review more reproducible and less biased. Consistent, thorough documentation is also key. Reviews of this type are not meant to be conducted by an individual but rather a (small) team of researchers. Systematic reviews are widely used in the health sciences, often to find a generalized conclusion from multiple evidence-based studies. 

Meta-Analysis

A systematic method that uses statistics to analyze the data from numerous studies. The researchers combine the data from studies with similar data types and analyze them as a single, expanded dataset. Meta-analyses are a type of systematic review.

Scoping Review

A scoping review employs the systematic review methodology to explore a broader topic or question rather than a specific and answerable one, as is generally the case with a systematic review. Authors of these types of reviews seek to collect and categorize the existing literature so as to identify any gaps.

Rapid Review

Rapid reviews are systematic reviews conducted under a time constraint. Researchers make use of workarounds to complete the review quickly (e.g., only looking at English-language publications), which can lead to a less thorough and more biased review. 

Narrative Review

A traditional literature review that summarizes and synthesizes the findings of numerous original research articles. The purpose and scope of narrative literature reviews vary widely and do not follow a set protocol. Most literature reviews are narrative reviews. 

Umbrella Review

Umbrella reviews are, essentially, systematic reviews of systematic reviews. These compile evidence from multiple review studies into one usable document. 

Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal , vol. 26, no. 2, 2009, pp. 91-108. doi: 10.1111/j.1471-1842.2009.00848.x .

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Systematic Reviews

• What is a Systematic Review?

A systematic review is an evidence synthesis that uses explicit, reproducible methods to perform a comprehensive literature search and critical appraisal of individual studies and that uses appropriate statistical techniques to combine these valid studies.

Key Characteristics of a Systematic Review:

Generally, systematic reviews must have:

• a clearly stated set of objectives with pre-defined eligibility criteria for studies
• an explicit, reproducible methodology
• a systematic search that attempts to identify all studies that would meet the eligibility criteria
• an assessment of the validity of the findings of the included studies, for example through the assessment of the risk of bias
• a systematic presentation, and synthesis, of the characteristics and findings of the included studies.

A meta-analysis is a systematic review that uses quantitative methods to synthesize and summarize the pooled data from included studies.

Additional Information

• How-to Books
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• Cochrane Handbook For Systematic Reviews of Interventions Provides guidance to authors for the preparation of Cochrane Intervention reviews. Chapter 6 covers searching for reviews.
• Systematic Reviews: CRD’s Guidance for Undertaking Reviews in Health Care From The University of York Centre for Reviews and Dissemination: Provides practical guidance for undertaking evidence synthesis based on a thorough understanding of systematic review methodology. It presents the core principles of systematic reviewing, and in complementary chapters, highlights issues that are specific to reviews of clinical tests, public health interventions, adverse effects, and economic evaluations.
• Cornell, Sytematic Reviews and Evidence Synthesis Beyond the Health Sciences Video series geared for librarians but very informative about searching outside medicine.
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1.2.2  What is a systematic review?

A systematic review attempts to collate all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question.  It  uses explicit, systematic methods that are selected with a view to minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made (Antman 1992, Oxman 1993) . The key characteristics of a systematic review are:

a clearly stated set of objectives with pre-defined eligibility criteria for studies;

an explicit, reproducible methodology;

a systematic search that attempts to identify all studies that would meet the eligibility criteria;

an assessment of the validity of the findings of the included studies, for example through the assessment of risk of bias; and

a systematic presentation, and synthesis, of the characteristics and findings of the included studies.

Many systematic reviews contain meta-analyses. Meta-analysis is the use of statistical methods to summarize the results of independent studies (Glass 1976). By combining information from all relevant studies, meta-analyses can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review (see Chapter 9, Section 9.1.3 ). They also facilitate investigations of the consistency of evidence across studies, and the exploration of differences across studies.

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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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Systematic Reviews: What is a systematic review?

What is a systematic review.

• Planning your review
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A systematic review is a tightly structured literature review that focuses on a topic with strict research parameters. The methodology used to collect research has to be consistent in order to reduce misinterpretation and misrepresentation of the data.

To help you understand and conduct your systematic review we have produce a number of posts to help you: 

• Getting started with your systematic review
• Introduction to Health Science databases
• Planning your systematic review
• Using frameworks to structure your search
• Advanced search: making use of Boolean operators
• Systematic review: organising your keywords and subject terms
• Making use of MeSH and Suggested Subject Terms

You can access these and more from the Specialist Library Support online resources page .

What is a Systematic literature search?

A systematic literature search is a literature review on a database (such as Medline) which demonstrates that you have compiled a list of appropriate search terms and includes the structure of your search history which provides the evidence on which your assignment is based.

This is a less rigorous process than a systematic review. A systematic review usually covers a wider scope; you would be expected to look at all the available research in the area in question. For example, you would be expected to visit the Library if articles were only held in hard copy format, and where necessary obtain articles not held by the Library via the Inter-Library Loan service .

You may be told that you need to conduct a systematic review when in fact you just need to perform a literature search in a systematic manner. 

If you are unsure about the differences between a systematic review and a literature review take a look at this guide:  What’s in a Name? The difference between a Systematic Review and a Literature Review and Why it Matters .

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Systematic Review

What is a systematic review.

• Five other types of systematic review
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A systematic review is an authoritative account of existing evidence using reliable, objective, thorough and reproducible research practices.

It is a method of making sense of large bodies of information and contributes to the answers to questions about what works and what doesn't.

Systematic reviews map areas of uncertainty and identify where little or no relevant research has been done, but where new studies are needed.

It is a good idea to familiarise yourself with the systematic review process before beginning your review. You can do this by searching for other systematic reviews to look at as examples, by  reading a glossary of commonly used terms , and by learning how to distinguish between  types of systematic review.

Characteristics of a systematic review

Some characteristics, or features, of systematic reviews are:

• Clearly stated set of objectives with pre-defined eligibility criteria
• Explicit, reproducible methodology
• A systematic search that attempts to identify all studies that would meet the eligibility criteria
• Assesses the validity of the findings, for example assessing the risk of bias
• Systematic presentation and synthesis of the findings of the included studies. (Cochrane Handbook for Systematic Reviews of Interventions, 2008, p. 6).

Watch this video from the Cochrane Library for more information about systematic reviews.

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• Korean J Anesthesiol
• v.71(2); 2018 Apr

Introduction to systematic review and meta-analysis

1 Department of Anesthesiology and Pain Medicine, Inje University Seoul Paik Hospital, Seoul, Korea

2 Department of Anesthesiology and Pain Medicine, Chung-Ang University College of Medicine, Seoul, Korea

Systematic reviews and meta-analyses present results by combining and analyzing data from different studies conducted on similar research topics. In recent years, systematic reviews and meta-analyses have been actively performed in various fields including anesthesiology. These research methods are powerful tools that can overcome the difficulties in performing large-scale randomized controlled trials. However, the inclusion of studies with any biases or improperly assessed quality of evidence in systematic reviews and meta-analyses could yield misleading results. Therefore, various guidelines have been suggested for conducting systematic reviews and meta-analyses to help standardize them and improve their quality. Nonetheless, accepting the conclusions of many studies without understanding the meta-analysis can be dangerous. Therefore, this article provides an easy introduction to clinicians on performing and understanding meta-analyses.

Introduction

A systematic review collects all possible studies related to a given topic and design, and reviews and analyzes their results [ 1 ]. During the systematic review process, the quality of studies is evaluated, and a statistical meta-analysis of the study results is conducted on the basis of their quality. A meta-analysis is a valid, objective, and scientific method of analyzing and combining different results. Usually, in order to obtain more reliable results, a meta-analysis is mainly conducted on randomized controlled trials (RCTs), which have a high level of evidence [ 2 ] ( Fig. 1 ). Since 1999, various papers have presented guidelines for reporting meta-analyses of RCTs. Following the Quality of Reporting of Meta-analyses (QUORUM) statement [ 3 ], and the appearance of registers such as Cochrane Library’s Methodology Register, a large number of systematic literature reviews have been registered. In 2009, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [ 4 ] was published, and it greatly helped standardize and improve the quality of systematic reviews and meta-analyses [ 5 ].

Levels of evidence.

In anesthesiology, the importance of systematic reviews and meta-analyses has been highlighted, and they provide diagnostic and therapeutic value to various areas, including not only perioperative management but also intensive care and outpatient anesthesia [6–13]. Systematic reviews and meta-analyses include various topics, such as comparing various treatments of postoperative nausea and vomiting [ 14 , 15 ], comparing general anesthesia and regional anesthesia [ 16 – 18 ], comparing airway maintenance devices [ 8 , 19 ], comparing various methods of postoperative pain control (e.g., patient-controlled analgesia pumps, nerve block, or analgesics) [ 20 – 23 ], comparing the precision of various monitoring instruments [ 7 ], and meta-analysis of dose-response in various drugs [ 12 ].

Thus, literature reviews and meta-analyses are being conducted in diverse medical fields, and the aim of highlighting their importance is to help better extract accurate, good quality data from the flood of data being produced. However, a lack of understanding about systematic reviews and meta-analyses can lead to incorrect outcomes being derived from the review and analysis processes. If readers indiscriminately accept the results of the many meta-analyses that are published, incorrect data may be obtained. Therefore, in this review, we aim to describe the contents and methods used in systematic reviews and meta-analyses in a way that is easy to understand for future authors and readers of systematic review and meta-analysis.

Study Planning

It is easy to confuse systematic reviews and meta-analyses. A systematic review is an objective, reproducible method to find answers to a certain research question, by collecting all available studies related to that question and reviewing and analyzing their results. A meta-analysis differs from a systematic review in that it uses statistical methods on estimates from two or more different studies to form a pooled estimate [ 1 ]. Following a systematic review, if it is not possible to form a pooled estimate, it can be published as is without progressing to a meta-analysis; however, if it is possible to form a pooled estimate from the extracted data, a meta-analysis can be attempted. Systematic reviews and meta-analyses usually proceed according to the flowchart presented in Fig. 2 . We explain each of the stages below.

Flowchart illustrating a systematic review.

Formulating research questions

A systematic review attempts to gather all available empirical research by using clearly defined, systematic methods to obtain answers to a specific question. A meta-analysis is the statistical process of analyzing and combining results from several similar studies. Here, the definition of the word “similar” is not made clear, but when selecting a topic for the meta-analysis, it is essential to ensure that the different studies present data that can be combined. If the studies contain data on the same topic that can be combined, a meta-analysis can even be performed using data from only two studies. However, study selection via a systematic review is a precondition for performing a meta-analysis, and it is important to clearly define the Population, Intervention, Comparison, Outcomes (PICO) parameters that are central to evidence-based research. In addition, selection of the research topic is based on logical evidence, and it is important to select a topic that is familiar to readers without clearly confirmed the evidence [ 24 ].

Protocols and registration

In systematic reviews, prior registration of a detailed research plan is very important. In order to make the research process transparent, primary/secondary outcomes and methods are set in advance, and in the event of changes to the method, other researchers and readers are informed when, how, and why. Many studies are registered with an organization like PROSPERO ( http://www.crd.york.ac.uk/PROSPERO/ ), and the registration number is recorded when reporting the study, in order to share the protocol at the time of planning.

Defining inclusion and exclusion criteria

Information is included on the study design, patient characteristics, publication status (published or unpublished), language used, and research period. If there is a discrepancy between the number of patients included in the study and the number of patients included in the analysis, this needs to be clearly explained while describing the patient characteristics, to avoid confusing the reader.

Literature search and study selection

In order to secure proper basis for evidence-based research, it is essential to perform a broad search that includes as many studies as possible that meet the inclusion and exclusion criteria. Typically, the three bibliographic databases Medline, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL) are used. In domestic studies, the Korean databases KoreaMed, KMBASE, and RISS4U may be included. Effort is required to identify not only published studies but also abstracts, ongoing studies, and studies awaiting publication. Among the studies retrieved in the search, the researchers remove duplicate studies, select studies that meet the inclusion/exclusion criteria based on the abstracts, and then make the final selection of studies based on their full text. In order to maintain transparency and objectivity throughout this process, study selection is conducted independently by at least two investigators. When there is a inconsistency in opinions, intervention is required via debate or by a third reviewer. The methods for this process also need to be planned in advance. It is essential to ensure the reproducibility of the literature selection process [ 25 ].

Quality of evidence

However, well planned the systematic review or meta-analysis is, if the quality of evidence in the studies is low, the quality of the meta-analysis decreases and incorrect results can be obtained [ 26 ]. Even when using randomized studies with a high quality of evidence, evaluating the quality of evidence precisely helps determine the strength of recommendations in the meta-analysis. One method of evaluating the quality of evidence in non-randomized studies is the Newcastle-Ottawa Scale, provided by the Ottawa Hospital Research Institute 1) . However, we are mostly focusing on meta-analyses that use randomized studies.

If the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) system ( http://www.gradeworkinggroup.org/ ) is used, the quality of evidence is evaluated on the basis of the study limitations, inaccuracies, incompleteness of outcome data, indirectness of evidence, and risk of publication bias, and this is used to determine the strength of recommendations [ 27 ]. As shown in Table 1 , the study limitations are evaluated using the “risk of bias” method proposed by Cochrane 2) . This method classifies bias in randomized studies as “low,” “high,” or “unclear” on the basis of the presence or absence of six processes (random sequence generation, allocation concealment, blinding participants or investigators, incomplete outcome data, selective reporting, and other biases) [ 28 ].

The Cochrane Collaboration’s Tool for Assessing the Risk of Bias [ 28 ]

Data extraction

Two different investigators extract data based on the objectives and form of the study; thereafter, the extracted data are reviewed. Since the size and format of each variable are different, the size and format of the outcomes are also different, and slight changes may be required when combining the data [ 29 ]. If there are differences in the size and format of the outcome variables that cause difficulties combining the data, such as the use of different evaluation instruments or different evaluation timepoints, the analysis may be limited to a systematic review. The investigators resolve differences of opinion by debate, and if they fail to reach a consensus, a third-reviewer is consulted.

Data Analysis

The aim of a meta-analysis is to derive a conclusion with increased power and accuracy than what could not be able to achieve in individual studies. Therefore, before analysis, it is crucial to evaluate the direction of effect, size of effect, homogeneity of effects among studies, and strength of evidence [ 30 ]. Thereafter, the data are reviewed qualitatively and quantitatively. If it is determined that the different research outcomes cannot be combined, all the results and characteristics of the individual studies are displayed in a table or in a descriptive form; this is referred to as a qualitative review. A meta-analysis is a quantitative review, in which the clinical effectiveness is evaluated by calculating the weighted pooled estimate for the interventions in at least two separate studies.

The pooled estimate is the outcome of the meta-analysis, and is typically explained using a forest plot ( Figs. 3 and ​ and4). 4 ). The black squares in the forest plot are the odds ratios (ORs) and 95% confidence intervals in each study. The area of the squares represents the weight reflected in the meta-analysis. The black diamond represents the OR and 95% confidence interval calculated across all the included studies. The bold vertical line represents a lack of therapeutic effect (OR = 1); if the confidence interval includes OR = 1, it means no significant difference was found between the treatment and control groups.

Forest plot analyzed by two different models using the same data. (A) Fixed-effect model. (B) Random-effect model. The figure depicts individual trials as filled squares with the relative sample size and the solid line as the 95% confidence interval of the difference. The diamond shape indicates the pooled estimate and uncertainty for the combined effect. The vertical line indicates the treatment group shows no effect (OR = 1). Moreover, if the confidence interval includes 1, then the result shows no evidence of difference between the treatment and control groups.

Forest plot representing homogeneous data.

Dichotomous variables and continuous variables

In data analysis, outcome variables can be considered broadly in terms of dichotomous variables and continuous variables. When combining data from continuous variables, the mean difference (MD) and standardized mean difference (SMD) are used ( Table 2 ).

Summary of Meta-analysis Methods Available in RevMan [ 28 ]

The MD is the absolute difference in mean values between the groups, and the SMD is the mean difference between groups divided by the standard deviation. When results are presented in the same units, the MD can be used, but when results are presented in different units, the SMD should be used. When the MD is used, the combined units must be shown. A value of “0” for the MD or SMD indicates that the effects of the new treatment method and the existing treatment method are the same. A value lower than “0” means the new treatment method is less effective than the existing method, and a value greater than “0” means the new treatment is more effective than the existing method.

When combining data for dichotomous variables, the OR, risk ratio (RR), or risk difference (RD) can be used. The RR and RD can be used for RCTs, quasi-experimental studies, or cohort studies, and the OR can be used for other case-control studies or cross-sectional studies. However, because the OR is difficult to interpret, using the RR and RD, if possible, is recommended. If the outcome variable is a dichotomous variable, it can be presented as the number needed to treat (NNT), which is the minimum number of patients who need to be treated in the intervention group, compared to the control group, for a given event to occur in at least one patient. Based on Table 3 , in an RCT, if x is the probability of the event occurring in the control group and y is the probability of the event occurring in the intervention group, then x = c/(c + d), y = a/(a + b), and the absolute risk reduction (ARR) = x − y. NNT can be obtained as the reciprocal, 1/ARR.

Calculation of the Number Needed to Treat in the Dichotomous table

Fixed-effect models and random-effect models

In order to analyze effect size, two types of models can be used: a fixed-effect model or a random-effect model. A fixed-effect model assumes that the effect of treatment is the same, and that variation between results in different studies is due to random error. Thus, a fixed-effect model can be used when the studies are considered to have the same design and methodology, or when the variability in results within a study is small, and the variance is thought to be due to random error. Three common methods are used for weighted estimation in a fixed-effect model: 1) inverse variance-weighted estimation 3) , 2) Mantel-Haenszel estimation 4) , and 3) Peto estimation 5) .

A random-effect model assumes heterogeneity between the studies being combined, and these models are used when the studies are assumed different, even if a heterogeneity test does not show a significant result. Unlike a fixed-effect model, a random-effect model assumes that the size of the effect of treatment differs among studies. Thus, differences in variation among studies are thought to be due to not only random error but also between-study variability in results. Therefore, weight does not decrease greatly for studies with a small number of patients. Among methods for weighted estimation in a random-effect model, the DerSimonian and Laird method 6) is mostly used for dichotomous variables, as the simplest method, while inverse variance-weighted estimation is used for continuous variables, as with fixed-effect models. These four methods are all used in Review Manager software (The Cochrane Collaboration, UK), and are described in a study by Deeks et al. [ 31 ] ( Table 2 ). However, when the number of studies included in the analysis is less than 10, the Hartung-Knapp-Sidik-Jonkman method 7) can better reduce the risk of type 1 error than does the DerSimonian and Laird method [ 32 ].

Fig. 3 shows the results of analyzing outcome data using a fixed-effect model (A) and a random-effect model (B). As shown in Fig. 3 , while the results from large studies are weighted more heavily in the fixed-effect model, studies are given relatively similar weights irrespective of study size in the random-effect model. Although identical data were being analyzed, as shown in Fig. 3 , the significant result in the fixed-effect model was no longer significant in the random-effect model. One representative example of the small study effect in a random-effect model is the meta-analysis by Li et al. [ 33 ]. In a large-scale study, intravenous injection of magnesium was unrelated to acute myocardial infarction, but in the random-effect model, which included numerous small studies, the small study effect resulted in an association being found between intravenous injection of magnesium and myocardial infarction. This small study effect can be controlled for by using a sensitivity analysis, which is performed to examine the contribution of each of the included studies to the final meta-analysis result. In particular, when heterogeneity is suspected in the study methods or results, by changing certain data or analytical methods, this method makes it possible to verify whether the changes affect the robustness of the results, and to examine the causes of such effects [ 34 ].

Heterogeneity

Homogeneity test is a method whether the degree of heterogeneity is greater than would be expected to occur naturally when the effect size calculated from several studies is higher than the sampling error. This makes it possible to test whether the effect size calculated from several studies is the same. Three types of homogeneity tests can be used: 1) forest plot, 2) Cochrane’s Q test (chi-squared), and 3) Higgins I 2 statistics. In the forest plot, as shown in Fig. 4 , greater overlap between the confidence intervals indicates greater homogeneity. For the Q statistic, when the P value of the chi-squared test, calculated from the forest plot in Fig. 4 , is less than 0.1, it is considered to show statistical heterogeneity and a random-effect can be used. Finally, I 2 can be used [ 35 ].

I 2 , calculated as shown above, returns a value between 0 and 100%. A value less than 25% is considered to show strong homogeneity, a value of 50% is average, and a value greater than 75% indicates strong heterogeneity.

Even when the data cannot be shown to be homogeneous, a fixed-effect model can be used, ignoring the heterogeneity, and all the study results can be presented individually, without combining them. However, in many cases, a random-effect model is applied, as described above, and a subgroup analysis or meta-regression analysis is performed to explain the heterogeneity. In a subgroup analysis, the data are divided into subgroups that are expected to be homogeneous, and these subgroups are analyzed. This needs to be planned in the predetermined protocol before starting the meta-analysis. A meta-regression analysis is similar to a normal regression analysis, except that the heterogeneity between studies is modeled. This process involves performing a regression analysis of the pooled estimate for covariance at the study level, and so it is usually not considered when the number of studies is less than 10. Here, univariate and multivariate regression analyses can both be considered.

Publication bias

Publication bias is the most common type of reporting bias in meta-analyses. This refers to the distortion of meta-analysis outcomes due to the higher likelihood of publication of statistically significant studies rather than non-significant studies. In order to test the presence or absence of publication bias, first, a funnel plot can be used ( Fig. 5 ). Studies are plotted on a scatter plot with effect size on the x-axis and precision or total sample size on the y-axis. If the points form an upside-down funnel shape, with a broad base that narrows towards the top of the plot, this indicates the absence of a publication bias ( Fig. 5A ) [ 29 , 36 ]. On the other hand, if the plot shows an asymmetric shape, with no points on one side of the graph, then publication bias can be suspected ( Fig. 5B ). Second, to test publication bias statistically, Begg and Mazumdar’s rank correlation test 8) [ 37 ] or Egger’s test 9) [ 29 ] can be used. If publication bias is detected, the trim-and-fill method 10) can be used to correct the bias [ 38 ]. Fig. 6 displays results that show publication bias in Egger’s test, which has then been corrected using the trim-and-fill method using Comprehensive Meta-Analysis software (Biostat, USA).

Funnel plot showing the effect size on the x-axis and sample size on the y-axis as a scatter plot. (A) Funnel plot without publication bias. The individual plots are broader at the bottom and narrower at the top. (B) Funnel plot with publication bias. The individual plots are located asymmetrically.

Funnel plot adjusted using the trim-and-fill method. White circles: comparisons included. Black circles: inputted comparisons using the trim-and-fill method. White diamond: pooled observed log risk ratio. Black diamond: pooled inputted log risk ratio.

Result Presentation

When reporting the results of a systematic review or meta-analysis, the analytical content and methods should be described in detail. First, a flowchart is displayed with the literature search and selection process according to the inclusion/exclusion criteria. Second, a table is shown with the characteristics of the included studies. A table should also be included with information related to the quality of evidence, such as GRADE ( Table 4 ). Third, the results of data analysis are shown in a forest plot and funnel plot. Fourth, if the results use dichotomous data, the NNT values can be reported, as described above.

The GRADE Evidence Quality for Each Outcome

N: number of studies, ROB: risk of bias, PON: postoperative nausea, POV: postoperative vomiting, PONV: postoperative nausea and vomiting, CI: confidence interval, RR: risk ratio, AR: absolute risk.

When Review Manager software (The Cochrane Collaboration, UK) is used for the analysis, two types of P values are given. The first is the P value from the z-test, which tests the null hypothesis that the intervention has no effect. The second P value is from the chi-squared test, which tests the null hypothesis for a lack of heterogeneity. The statistical result for the intervention effect, which is generally considered the most important result in meta-analyses, is the z-test P value.

A common mistake when reporting results is, given a z-test P value greater than 0.05, to say there was “no statistical significance” or “no difference.” When evaluating statistical significance in a meta-analysis, a P value lower than 0.05 can be explained as “a significant difference in the effects of the two treatment methods.” However, the P value may appear non-significant whether or not there is a difference between the two treatment methods. In such a situation, it is better to announce “there was no strong evidence for an effect,” and to present the P value and confidence intervals. Another common mistake is to think that a smaller P value is indicative of a more significant effect. In meta-analyses of large-scale studies, the P value is more greatly affected by the number of studies and patients included, rather than by the significance of the results; therefore, care should be taken when interpreting the results of a meta-analysis.

When performing a systematic literature review or meta-analysis, if the quality of studies is not properly evaluated or if proper methodology is not strictly applied, the results can be biased and the outcomes can be incorrect. However, when systematic reviews and meta-analyses are properly implemented, they can yield powerful results that could usually only be achieved using large-scale RCTs, which are difficult to perform in individual studies. As our understanding of evidence-based medicine increases and its importance is better appreciated, the number of systematic reviews and meta-analyses will keep increasing. However, indiscriminate acceptance of the results of all these meta-analyses can be dangerous, and hence, we recommend that their results be received critically on the basis of a more accurate understanding.

1) http://www.ohri.ca .

2) http://methods.cochrane.org/bias/assessing-risk-bias-included-studies .

3) The inverse variance-weighted estimation method is useful if the number of studies is small with large sample sizes.

4) The Mantel-Haenszel estimation method is useful if the number of studies is large with small sample sizes.

5) The Peto estimation method is useful if the event rate is low or one of the two groups shows zero incidence.

6) The most popular and simplest statistical method used in Review Manager and Comprehensive Meta-analysis software.

7) Alternative random-effect model meta-analysis that has more adequate error rates than does the common DerSimonian and Laird method, especially when the number of studies is small. However, even with the Hartung-Knapp-Sidik-Jonkman method, when there are less than five studies with very unequal sizes, extra caution is needed.

8) The Begg and Mazumdar rank correlation test uses the correlation between the ranks of effect sizes and the ranks of their variances [ 37 ].

9) The degree of funnel plot asymmetry as measured by the intercept from the regression of standard normal deviates against precision [ 29 ].

10) If there are more small studies on one side, we expect the suppression of studies on the other side. Trimming yields the adjusted effect size and reduces the variance of the effects by adding the original studies back into the analysis as a mirror image of each study.

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A high-quality systematic review is described as the most reliable source of evidence to guide clinical practice. The purpose of a systematic review is to deliver a meticulous summary of all the available primary research in response to a research question. A systematic review uses all the existing research and is sometime called ‘secondary research’ (research on research). They are often required by research funders to establish the state of existing knowledge and are frequently used in guideline development. Systematic review findings are often used within the …

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Systematic Literature Review: Easy Guide

WRONG. It turns out that typing “what is a systematic literature review” into Google will only overwhelm a new researcher! I came across plenty of journal articles that claimed to be explaining what an SLR was (and how that somehow differed from another term I was learning – a scoping review), but for the life of me I could not find a clear-cut set of instructions. All of the information seemed to be pitched at a level far above the one I was operating at, and I began to feel frustrated that I could not find a source that was putting this methodology into terms that the average person could understand. But I knew I needed to figure it out, so over the course of the next few weeks I read what felt like dozens of explainers and guides.

Eventually, my reading and furious note-taking paid off, because by the end of 2023 I had successfully completed my research, entitled “How are language barriers bridged in hospitals?: a systematic review” . But in the process, I had spoken to so many academics who also voiced their frustration that they couldn’t find explanations on how to conduct an SLR in clear lay terms, and so I knew I hadn’t been alone.

Something I feel VERY passionate about is that, as academics, we must be able to talk to people outside of academia, and that means that we need to be able to communicate complex ideas in easily digestible ways. Higher knowledge shouldn’t be reserved for people who have weeks to teach themselves a new research methodology, and I wanted to be able to explain an SLR to everyone, not just other researchers.

And so, I created this “ SLR: Easy Guide ” explainer for anyone and everyone who would like to conduct an SLR but has no idea where to start. If that’s you, please feel free to use this resource – and know that you aren’t alone as an early researcher who is learning things for the first time. We’ve all got to start somewhere, and we can make it easier on others by sharing what we’ve figured out the hard way!

What exactly is a systematic literature review (SLR)?

Ok, so you know how you need to do a literature review before you write a research paper? In that literature review, you are basically summarising what other researchers have said about your research topic so that you can show how your research is building on prior knowledge.

An SLR is different to that. An SLR is your research (your “experiment”, if you will). In an SLR, you read and analyse lots of different published journal articles in order to see patterns in already-published data. There’s an actual methodology that you have to use (which I detail in SLR: An Easy Guide ) in order to select these journal articles.

I haven’t heard of an SLR, but I’ve heard of a meta-analysis. What’s the difference?

Literally nothing. They mean the same thing! Surprise! Academia is fun and not at all confusing.

I’ve also heard of a scoping review. Is that the same as a systematic literature review?

In this case, there actually is a difference, albeit a relatively small one. The methodology for both types of reviews will be the same (whew!), but the reason for conducting one versus the other will be a bit different. Let me give you an example based on my own research. When I began looking into how hospitals manage linguistic diversity between patients and staff, I knew that there was already a lot of literature out there about the subject (generally having to do with the work of professional interpreters). I had four very specific research questions that I wanted to answer based on that literature. This is why I conducted a systematic review – because I already knew that I would be able to find existing research that could answer my questions.

HOWEVER, you might not know how much literature already exists on a given topic. Maybe your topic is fairly niche, so you haven’t seen much about it in publications. This is where a scoping review comes in. In conducting a scoping review, you’ll find out exactly how much literature on the topic already exists. In doing so, you’ll be able to make an argument for why a particular area of research should be looked into more.

If this still sounds confusing (totally understandable!), be sure to talk to a fabulous university librarian. They are really good at knowing the difference between the two!

Is there any kind of SLR “authority” that I should know about?

There sure is! There is an organisation called PRISMA (which stands for Preferred Reporting Items for Systematic Reviews and Meta-Analyses). You can go to their website for two very crucial items that you will need for your SLR: a checklist and a flow chart.

The PRISMA checklist is great because it tells you exactly what you need to include in your SLR. The PRISMA flow chart is what you include in your SLR to show why/how you included and excluded studies during your screening process (which you can see in steps 3 and 4 of my SLR: An Easy Guide  resource). But don’t worry, you don’t need to create the flow chart from scratch. If you use Covidence, the platform will create it for you. And speaking of Covidence…

This feels overwhelming! Is there one place I can go to manage all my SLR data easily?

Absolutely. I used Covidence , an online platform that essentially walks you through the SLR process. I would HIGHLY recommend using Covidence or a similar service to help you manage all your data in one place. Covidence will also automatically create your flow chart for you as you go through your screening process. What I especially liked about Covidence was that I was able to custom-create my data collection template based on my specific research questions. This made my data analysis much easier than it would have been without it!

What do I do if I’m still confused or feel like I don’t know how to do this?

Remember that every single one of us who goes on to do higher degree research feels like this. We don’t know what we don’t know! I’ve now completed two Masters degrees and am currently working on my PhD, and let me tell you, the learning curve is steep! But you know what? You can do it. Don’t be afraid to ask questions. Tell your supervisors and colleagues when you feel lost. Remind yourself that learning these research skills is just as important as the research itself. And when you get super stressed, grab a cup of coffee, stand in the sunshine and take a 10-minute break. You’ve got this!

Download and cite my free “SLR: An Easy Guide” resource

“ SLR: An Easy Guide ” is a free cheat sheet for your systematic literature review. You can download it here .

If you find it useful, please cite as:

Quick, B. (2024). Systematic Literature Review: An Easy Guide. Language on the Move . Retrieved from https://www.languageonthemove.com/systematic-literature-review-easy-guide

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Author Brynn Quick

Brynn Quick holds a Master of Applied Linguistics and a Master of Research from Macquarie University. For her PhD, also at Macquarie University, she is investigating how language barriers are bridged between patients and staff in Australian hospitals. Her linguistic interests are many and varied, and include sociolinguistics, anthropological linguistics, sociophonetics, and historical linguistics, particularly the history of English.

Join the discussion 3 Comments

This is really helpful! Thanks a lot!

Wow, Brynn! What a creative and relatable way to navigate an otherwise intimidating research method! Thanks for sharing your guide. Will definitely use it!

Thanks so much, Pia! I’m so glad you find it helpful!

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What is a Systematic Literature Review?

A systematic literature review (SLR) is an independent academic method that aims to identify and evaluate all relevant literature on a topic in order to derive conclusions about the question under consideration. "Systematic reviews are undertaken to clarify the state of existing research and the implications that should be drawn from this." (Feak & Swales, 2009, p. 3) An SLR can demonstrate the current state of research on a topic, while identifying gaps and areas requiring further research with regard to a given research question. A formal methodological approach is pursued in order to reduce distortions caused by an overly restrictive selection of the available literature and to increase the reliability of the literature selected (Tranfield, Denyer & Smart, 2003). A special aspect in this regard is the fact that a research objective is defined for the search itself and the criteria for determining what is to be included and excluded are defined prior to conducting the search. The search is mainly performed in electronic literature databases (such as Business Source Complete or Web of Science), but also includes manual searches (reviews of reference lists in relevant sources) and the identification of literature not yet published in order to obtain a comprehensive overview of a research topic.

An SLR protocol documents all the information gathered and the steps taken as part of an SLR in order to make the selection process transparent and reproducible. The PRISMA flow-diagram support you in making the selection process visible.

In an ideal scenario, experts from the respective research discipline, as well as experts working in the relevant field and in libraries, should be involved in setting the search terms . As a rule, the literature is selected by two or more reviewers working independently of one another. Both measures serve the purpose of increasing the objectivity of the literature selection. An SLR must, then, be more than merely a summary of a topic (Briner & Denyer, 2012). As such, it also distinguishes itself from “ordinary” surveys of the available literature. The following table shows the differences between an SLR and an “ordinary” literature review.

• Charts of BSWL workshop (pdf, 2.88 MB)
• Listen to the interview (mp4, 12.35 MB)

Differences to "common" literature reviews

What are the objectives of SLRs?

• Avoidance of research redundancies despite a growing amount of publications
• Identification of research areas, gaps and methods
• Input for evidence-based management, which allows to base management decisions on scientific methods and findings
• Identification of links between different areas of researc

Process steps of an SLR

A SLR has several process steps which are defined differently in the literature (Fink 2014, p. 4; Guba 2008, Transfield et al. 2003). We distinguish the following steps which are adapted to the economics and management research area:

1. Defining research questions

Briner & Denyer (2009, p. 347ff.) have developed the CIMO scheme to establish clearly formulated and answerable research questions in the field of economic sciences:

C – CONTEXT:  Which individuals, relationships, institutional frameworks and systems are being investigated?

I – Intervention:  The effects of which event, action or activity are being investigated?

M – Mechanisms:  Which mechanisms can explain the relationship between interventions and results? Under what conditions do these mechanisms take effect?

O – Outcomes:  What are the effects of the intervention? How are the results measured? What are intended and unintended effects?

The objective of the systematic literature review is used to formulate research questions such as “How can a project team be led effectively?”. Since there are numerous interpretations and constructs for “effective”, “leadership” and “project team”, these terms must be particularized.

With the aid of the scheme, the following concrete research questions can be derived with regard to this example:

Under what conditions (C) does leadership style (I) influence the performance of project teams (O)?

Which constructs have an effect upon the influence of leadership style (I) on a project team’s performance (O)?          

Research questions do not necessarily need to follow the CIMO scheme, but they should:

• ... be formulated in a clear, focused and comprehensible manner and be answerable;
• ... have been determined prior to carrying out the SLR;
• ... consist of general and specific questions.

As early as this stage, the criteria for inclusion and exclusion are also defined. The selection of the criteria must be well-grounded. This may include conceptual factors such as a geographical or temporal restrictions, congruent definitions of constructs, as well as quality criteria (journal impact factor > x).

2. Selecting databases and other research sources

The selection of sources must be described and explained in detail. The aim is to find a balance between the relevance of the sources (content-related fit) and the scope of the sources.

In the field of economic sciences, there are a number of literature databases that can be searched as part of an SLR. Some examples in this regard are:

• Business Source Complete
• ProQuest One Business
• EconBiz        

Our video " Selecting the right databases " explains how to find relevant databases for your topic.

Literature databases are an important source of research for SLRs, as they can minimize distortions caused by an individual literature selection (selection bias), while offering advantages for a systematic search due to their data structure. The aim is to find all database entries on a topic and thus keep the retrieval bias low (tutorial on retrieval bias ).  Besides articles from scientific journals, it is important to inlcude working papers, conference proceedings, etc to reduce the publication bias ( tutorial on publication bias ).

Our online self-study course " Searching economic databases " explains step 2 und 3.

3. Defining search terms

Once the literature databases and other research sources have been selected, search terms are defined. For this purpose, the research topic/questions is/are divided into blocks of terms of equal ranking. This approach is called the block-building method (Guba 2008, p. 63). The so-called document-term matrix, which lists topic blocks and search terms according to a scheme, is helpful in this regard. The aim is to identify as many different synonyms as possible for the partial terms. A precisely formulated research question facilitates the identification of relevant search terms. In addition, keywords from particularly relevant articles support the formulation of search terms.

A document-term matrix for the topic “The influence of management style on the performance of project teams” is shown in this example .

Identification of headwords and keywords

When setting search terms, a distinction must be made between subject headings and keywords, both of which are described below:

• appear in the title, abstract and/or text
• sometimes specified by the author, but in most cases automatically generated
• non-standardized
• different spellings and forms (singular/plural) must be searched separately

Subject headings

• describe the content
• are generated by an editorial team
• are listed in a standardized list (thesaurus)
• may comprise various keywords
• include different spellings
• database-specific

Subject headings are a standardized list of words that are generated by the specialists in charge of some databases. This so-called index of subject headings (thesaurus) helps searchers find relevant articles, since the headwords indicate the content of a publication. By contrast, an ordinary keyword search does not necessarily result in a content-related fit, since the database also displays articles in which, for example, a word appears once in the abstract, even though the article’s content does not cover the topic.

Nevertheless, searches using both headwords and keywords should be conducted, since some articles may not yet have been assigned headwords, or errors may have occurred during the assignment of headwords. 

To add headwords to your search in the Business Source Complete database, please select the Thesaurus tab at the top. Here you can find headwords in a new search field and integrate them into your search query. In the search history, headwords are marked with the addition DE (descriptor).

The EconBiz database of the German National Library of Economics (ZBW – Leibniz Information Centre for Economics), which also contains German-language literature, has created its own index of subject headings with the STW Thesaurus for Economics . Headwords are integrated into the search by being used in the search query.

Since the indexes of subject headings divide terms into synonyms, generic terms and sub-aspects, they facilitate the creation of a document-term matrix. For this purpose it is advisable to specify in the document-term matrix the origin of the search terms (STW Thesaurus for Economics, Business Source Complete, etc.).

Searching in literature databases

Once the document-term matrix has been defined, the search in literature databases begins. It is recommended to enter each word of the document-term matrix individually into the database in order to obtain a good overview of the number of hits per word. Finally, all the words contained in a block of terms are linked with the Boolean operator OR and thereby a union of all the words is formed. The latter are then linked with each other using the Boolean operator AND. In doing so, each block should be added individually in order to see to what degree the number of hits decreases.

Since the search query must be set up separately for each database, tools such as  LitSonar  have been developed to enable a systematic search across different databases. LitSonar was created by  Professor Dr. Ali Sunyaev (Institute of Applied Informatics and Formal Description Methods – AIFB) at the Karlsruhe Institute of Technology.

Advanced search

Certain database-specific commands can be used to refine a search, for example, by taking variable word endings into account (*) or specifying the distance between two words, etc. Our overview shows the most important search commands for our top databases.

Additional searches in sources other than literature databases

In addition to literature databases, other sources should also be searched. Fink (2014, p. 27) lists the following reasons for this:

• the topic is new and not yet included in indexes of subject headings;
• search terms are not used congruently in articles because uniform definitions do not exist;
• some studies are still in the process of being published, or have been completed, but not published.

Therefore, further search strategies are manual search, bibliographic analysis, personal contacts and academic networks (Briner & Denyer, p. 349). Manual search means that you go through the source information of relevant articles and supplement your hit list accordingly. In addition, you should conduct a targeted search for so-called gray literature, that is, literature not distributed via the book trade, such as working papers from specialist areas and conference reports. By including different types of publications, the so-called publication bias (DBWM video “Understanding publication bias” ) – that is, distortions due to exclusive use of articles from peer-reviewed journals – should be kept to a minimum.

The PRESS-Checklist can support you to check the correctness of your search terms.

4. Merging hits from different databases

In principle, large amounts of data can be easily collected, structured and sorted with data processing programs such as Excel. Another option is to use reference management programs such as EndNote, Citavi or Zotero. The Saxon State and University Library Dresden (SLUB Dresden) provides an  overview of current reference management programs  . Software for qualitative data analysis such as NVivo is equally suited for data processing. A comprehensive overview of the features of different tools that support the SLR process can be found in Bandara et al. (2015).

Our online-self study course "Managing literature with Citavi" shows you how to use the reference management software Citavi.

When conducting an SLR, you should specify for each hit the database from which it originates and the date on which the query was made. In addition, you should always indicate how many hits you have identified in the various databases or, for example, by manual search.

Exporting data from literature databases

Exporting from literature databases is very easy. In  Business Source Complete  , you must first click on the “Share” button in the hit list, then “Email a link to download exported results” at the very bottom and then select the appropriate format for the respective literature program.

Exporting data from the literature database  EconBiz  is somewhat more complex. Here you must first create a marked list and then select each hit individually and add it to the marked list. Afterwards, articles on the list can be exported.

After merging all hits from the various databases, duplicate entries (duplicates) are deleted.

5. Applying inclusion and exclusion criteria

All publications are evaluated in the literature management program applying the previously defined criteria for inclusion and exclusion. Only those sources that survive this selection process will subsequently be analyzed. The review process and inclusion criteria should be tested with a small sample and adjustments made if necessary before applying it to all articles. In the ideal case, even this selection would be carried out by more than one person, with each working independently of one another. It needs to be made clear how discrepancies between reviewers are dealt with. 

The review of the criteria for inclusion and exclusion is primarily based on the title, abstract and subject headings in the databases, as well as on the keywords provided by the authors of a publication in the first step. In a second step the whole article / source will be read.

You can create tag words for the inclusion and exclusion in your literature management tool to keep an overview.

In addition to the common literature management tools, you can also use software tools that have been developed to support SLRs. The central library of the university in Zurich has published an overview and evaluation of different tools based on a survey among researchers. --> View SLR tools

The selection process needs to be made transparent. The PRISMA flow diagram supports the visualization of the number of included / excluded studies.

Forward and backward search

Should it become apparent that the number of sources found is relatively small, or if you wish to proceed with particular thoroughness, a forward-and-backward search based on the sources found is recommendable (Webster & Watson 2002, p. xvi). A backward search means going through the bibliographies of the sources found. A forward search, by contrast, identifies articles that have cited the relevant publications. The Web of Science and Scopus databases can be used to perform citation analyses.

6. Perform the review

As the next step, the remaining titles are analyzed as to their content by reading them several times in full. Information is extracted according to defined criteria and the quality of the publications is evaluated. If the data extraction is carried out by more than one person, a training ensures that there will be no differences between the reviewers.

Depending on the research questions there exist diffent methods for data abstraction (content analysis, concept matrix etc.). A so-called concept matrix can be used to structure the content of information (Webster & Watson 2002, p. xvii). The image to the right gives an example of a concept matrix according to Becker (2014).

Particularly in the field of economic sciences, the evaluation of a study’s quality cannot be performed according to a generally valid scheme, such as those existing in the field of medicine, for instance. Quality assessment therefore depends largely on the research questions.

Based on the findings of individual studies, a meta-level is then applied to try to understand what similarities and differences exist between the publications, what research gaps exist, etc. This may also result in the development of a theoretical model or reference framework.

Example concept matrix (Becker 2013) on the topic Business Process Management

7. Synthesizing results

Once the review has been conducted, the results must be compiled and, on the basis of these, conclusions derived with regard to the research question (Fink 2014, p. 199ff.). This includes, for example, the following aspects:

• historical development of topics (histogram, time series: when, and how frequently, did publications on the research topic appear?);
• overview of journals, authors or specialist disciplines dealing with the topic;
• comparison of applied statistical methods;
• topics covered by research;
• identifying research gaps;
• developing a reference framework;
• developing constructs;
• performing a meta-analysis: comparison of the correlations of the results of different empirical studies (see for example Fink 2014, p. 203 on conducting meta-analyses)

Publications about the method

Bandara, W., Furtmueller, E., Miskon, S., Gorbacheva, E., & Beekhuyzen, J. (2015). Achieving Rigor in Literature Reviews: Insights from Qualitative Data Analysis and Tool-Support.  Communications of the Association for Information Systems . 34(8), 154-204.

Booth, A., Papaioannou, D., and Sutton, A. (2012)  Systematic approaches to a successful literature review.  London: Sage.

Briner, R. B., & Denyer, D. (2012). Systematic Review and Evidence Synthesis as a Practice and Scholarship Tool. In Rousseau, D. M. (Hrsg.),  The Oxford Handbook of Evidenence Based Management . (S. 112-129). Oxford: Oxford University Press.

Durach, C. F., Wieland, A., & Machuca, Jose A. D. (2015). Antecedents and dimensions of supply chain robustness: a systematic literature review . International Journal of Physical Distribution & Logistic Management , 46 (1/2), 118-137. doi:  https://doi.org/10.1108/IJPDLM-05-2013-0133

Feak, C. B., & Swales, J. M. (2009). Telling a Research Story: Writing a Literature Review.  English in Today's Research World 2.  Ann Arbor: University of Michigan Press. doi:  10.3998/mpub.309338

Fink, A. (2014).  Conducting Research Literature Reviews: From the Internet to Paper  (4. Aufl.). Los Angeles, London, New Delhi, Singapore, Washington DC: Sage Publication.

Fisch, C., & Block, J. (2018). Six tips for your (systematic) literature review in business and management research.  Management Review Quarterly,  68, 103–106 (2018).  doi.org/10.1007/s11301-018-0142-x

Guba, B. (2008). Systematische Literaturrecherche.  Wiener Medizinische Wochenschrift , 158 (1-2), S. 62-69. doi:  doi.org/10.1007/s10354-007-0500-0  Hart, C.  Doing a literature review: releasing the social science research imagination.  London: Sage.

Jesson, J. K., Metheson, L. & Lacey, F. (2011).  Doing your Literature Review - traditional and Systematic Techniques . Los Angeles, London, New Delhi, Singapore, Washington DC: Sage Publication.

Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ 2021;372:n71. doi: 10.1136/bmj.n71.

Petticrew, M. and Roberts, H. (2006).  Systematic Reviews in the Social Sciences: A Practical Guide . Oxford:Blackwell. Ridley, D. (2012).  The literature review: A step-by-step guide . 2nd edn. London: Sage. 

Chang, W. and Taylor, S.A. (2016), The Effectiveness of Customer Participation in New Product Development: A Meta-Analysis,  Journal of Marketing , American Marketing Association, Los Angeles, CA, Vol. 80 No. 1, pp. 47–64.

Tranfield, D., Denyer, D. & Smart, P. (2003). Towards a methodology for developing evidence-informed management knowledge by means of systematic review.  British Journal of Management , 14 (3), S. 207-222. doi:  https://doi.org/10.1111/1467-8551.00375

Webster, J., & Watson, R. T. (2002). Analyzing the Past to Prepare for the Future: Writing a Literature Review.  Management Information Systems Quarterly , 26(2), xiii-xxiii.  http://www.jstor.org/stable/4132319

Durach, C. F., Wieland, A. & Machuca, Jose. A. D. (2015). Antecedents and dimensions of supply chain robustness: a systematic literature review. International Journal of Physical Distribution & Logistics Management, 45(1/2), 118 – 137.

What is particularly good about this example is that search terms were defined by a number of experts and the review was conducted by three researchers working independently of one another. Furthermore, the search terms used have been very well extracted and the procedure of the literature selection very well described.

On the downside, the restriction to English-language literature brings the language bias into play, even though the authors consider it to be insignificant for the subject area.

Bos-Nehles, A., Renkema, M. & Janssen, M. (2017). HRM and innovative work behaviour: a systematic literature review. Personnel Review, 46(7), pp. 1228-1253

• Only very specific keywords used
• No precise information on how the review process was carried out (who reviewed articles?)
• Only journals with impact factor (publication bias)

Jia, F., Orzes, G., Sartor, M. & Nassimbeni, G. (2017). Global sourcing strategy and structure: towards a conceptual framework. International Journal of Operations & Production Management, 37(7), 840-864

• Research questions are explicitly presented
• Search string very detailed
• Exact description of the review process
• 2 persons conducted the review independently of each other

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The difference between a systematic review and a literature review

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Home | Blog | Best Practice | The difference between a systematic review and a literature review

Covidence takes a look at the difference between the two

Most of us are familiar with the terms systematic review and literature review. Both review types synthesise evidence and provide summary information. So what are the differences? What does systematic mean? And which approach is best 🤔 ?

‘ Systematic ‘ describes the review’s methods. It means that they are transparent, reproducible and defined before the search gets underway. That’s important because it helps to minimise the bias that would result from cherry-picking studies in a non-systematic way. 

This brings us to literature reviews. Literature reviews don’t usually apply the same rigour in their methods. That’s because, unlike systematic reviews, they don’t aim to produce an answer to a clinical question. Literature reviews can provide context or background information for a new piece of research. They can also stand alone as a general guide to what is already known about a particular topic. 

Interest in systematic reviews has grown in recent years and the frequency of ‘systematic reviews’ in Google books has overtaken ‘literature reviews’ (with all the usual Ngram Viewer warnings – it searches around 6% of all books, no journals). 

Let’s take a look at the two review types in more detail to highlight some key similarities and differences 👀.

🙋🏾‍♂️ What is a systematic review?

Systematic reviews ask a specific question about the effectiveness of a treatment and answer it by summarising evidence that meets a set of pre-specified criteria. 

The process starts with a research question and a protocol or research plan. A review team searches for studies to answer the question using a highly sensitive search strategy. The retrieved studies are then screened for eligibility using the inclusion and exclusion criteria (this is done by at least two people working independently). Next, the reviewers extract the relevant data and assess the quality of the included studies. Finally, the review team synthesises the extracted study data and presents the results. The process is shown in figure 2 .

The results of a systematic review can be presented in many ways and the choice will depend on factors such as the type of data. Some reviews use meta-analysis to produce a statistical summary of effect estimates. Other reviews use narrative synthesis to present a textual summary.

Covidence accelerates the screening, data extraction, and quality assessment stages of your systematic review. It provides simple workflows and easy collaboration with colleagues around the world.

When is it appropriate to do a systematic review?

If you have a clinical question about the effectiveness of a particular treatment or treatments, you could answer it by conducting a systematic review. Systematic reviews in clinical medicine often follow the PICO framework, which stands for:

👦 Population (or patients)

💊 Intervention

💊 Comparison

Here’s a typical example of a systematic review title that uses the PICO framework: Alarms [intervention] versus drug treatments [comparison] for the prevention of nocturnal enuresis [outcome] in children [population]

Key attributes

• Systematic reviews follow prespecified methods
• The methods are explicit and replicable
• The review team assesses the quality of the evidence and attempts to minimise bias
• Results and conclusions are based on the evidence

🙋🏻‍♀️ What is a literature review?

Literature reviews provide an overview of what is known about a particular topic. They evaluate the material, rather than simply restating it, but the methods used to do this are not usually prespecified and they are not described in detail in the review. The search might be comprehensive but it does not aim to be exhaustive. Literature reviews are also referred to as narrative reviews.

Literature reviews use a topical approach and often take the form of a discussion. Precision and replicability are not the focus, rather the author seeks to demonstrate their understanding and perhaps also present their work in the context of what has come before. Often, this sort of synthesis does not attempt to control for the author’s own bias. The results or conclusion of a literature review is likely to be presented using words rather than statistical methods.

When is it appropriate to do a literature review?

We’ve all written some form of literature review: they are a central part of academic research ✍🏾. Literature reviews often form the introduction to a piece of writing, to provide the context. They can also be used to identify gaps in the literature and the need to fill them with new research 📚.

• Literature reviews take a thematic approach
• They do not specify inclusion or exclusion criteria
• They do not answer a clinical question
• The conclusions might be influenced by the author’s own views

🙋🏽 Ok, but what is a systematic literature review?

A quick internet search retrieves a cool 200 million hits for ‘systematic literature review’. What strange hybrid is this 🤯🤯 ?

Systematic review methodology has its roots in evidence-based medicine but it quickly gained traction in other areas – the social sciences for example – where researchers recognise the value of being methodical and minimising bias. Systematic review methods are increasingly applied to the more traditional types of review, including literature reviews, hence the proliferation of terms like ‘systematic literature review’ and many more.

Beware of the labels 🚨. The terminology used to describe review types can vary by discipline and changes over time. To really understand how any review was done you will need to examine the methods critically and make your own assessment of the quality and reliability of each synthesis 🤓.

Review methods are evolving constantly as researchers find new ways to meet the challenge of synthesising the evidence. Systematic review methods have influenced many other review types, including the traditional literature review. 

Covidence is a web-based tool that saves you time at the screening, selection, data extraction and quality assessment stages of your systematic review. It supports easy collaboration across teams and provides a clear overview of task status.

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Laura Mellor. Portsmouth, UK

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Types of Literature Reviews

Literature reviews are comprehensive summaries and syntheses of the previous research on a given topic.

The review purpose, methods used, and the results produced vary among different kinds of literature reviews. Some of the common types of literature review are detailed below.

Common Types of Literature Reviews 1

Narrative (literature) review.

• A broad term referring to reviews with a wide scope and non-standardized methodology
• Search strategies, comprehensiveness of literature search, time range covered and method of synthesis will vary and do not follow an established protocol

Integrative Review

• A type of literature review based on a systematic, structured literature search
• Often has a broadly defined purpose or review question
• Seeks to generate or refine and theory or hypothesis and/or develop a holistic understanding of a topic of interest
• Relies on diverse sources of data (e.g. empirical, theoretical or methodological literature; qualitative or quantitative studies)

Systematic Review

• Systematically and transparently collects and categorize existing evidence on a question of scientific, policy or management importance
• Follows a research protocol that is established  a priori
• Some sub-types of systematic reviews include: SRs of intervention effectiveness, diagnosis, prognosis, etiology, qualitative evidence, economic evidence, and more.
• Time-intensive and often takes months to a year or more to complete 
• The most commonly referred to type of evidence synthesis; sometimes confused as a blanket term for other types of reviews

Meta-Analysis

• Statistical technique for combining the findings from disparate quantitative studies
• Uses statistical methods to objectively evaluate, synthesize, and summarize results
• Often conducted as part of a systematic review

Scoping Review

• Systematically and transparently collects and categorizes existing evidence on a broad question of scientific, policy or management importance
• Seeks to identify research gaps, identify key concepts and characteristics of the literature and/or examine how research is conducted on a topic of interest
• Useful when the complexity or heterogeneity of the body of literature does not lend itself to a precise systematic review
• Useful if authors do not have a single, precise review question
• May critically evaluate existing evidence, but does not attempt to synthesize the results in the way a systematic review would 
• May take longer than a systematic review

Rapid Review

• Applies a systematic review methodology within a time-constrained setting
• Employs methodological "shortcuts" (e.g., limiting search terms and the scope of the literature search), at the risk of introducing bias
• Useful for addressing issues requiring quick decisions, such as developing policy recommendations

Umbrella Review

• Reviews other systematic reviews on a topic
• Often defines a broader question than is typical of a traditional systematic review
• Most useful when there are competing interventions to consider

1. Adapted from:

Eldermire, E. (2021, November 15). A guide to evidence synthesis: Types of evidence synthesis. Cornell University LibGuides.  https://guides.library.cornell.edu/evidence-synthesis/types

Nolfi, D. (2021, October 6). Integrative Review: Systematic vs. Scoping vs. Integrative. Duquesne University LibGuides.  https://guides.library.duq.edu/c.php?g=1055475&p=7725920

Delaney, L. (2021, November 24). Systematic reviews: Other review types. UniSA LibGuides.  https://guides.library.unisa.edu.au/SystematicReviews/OtherReviewTypes

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