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Systematic Review: Review types

This guide presents tools and advice for conducting systematic reviews.

Review Types

Systematic Reviews are only one type of team based review and may not be the correct review type for the question you want to answer. Use this decision tree to help decide which is the best review for your question. 

Graphic image of a decision tree for determining which review type is best for your research question and goals.

Figure 1. Review decision tree. Click the image for a larger version. (adapted from Cornell University Review Methodology Decision Tree https://guides.library.cornell.edu/ld.php?content_id=52561085)

 

Accessible version:

Review Type Decision Tree

What Type of Review is Right for You?
  1. Do you want to gather all the evidence on a particular research topic?
    1. No. You should undertake a Literature or Narrative Review.
    2. Yes. Continue to question 2.
  2. Do you have three or more people to work on the review?
    1. No. More intensive reviews usually require a multi-person team for unbiased article screening.
    2. Yes. Continue to question 3.
  3. Do you have twelve to eighteen months to complete a review?
    1. No. You should undertake a Rapid Review.
    2. Yes. Continue to question 4.
  4. Do you have a broad topic of multiple research questions?
    1. Yes. You should undertake a Scoping Review.
    2. No. Continue to question 5.
  5. Do you want to review other published systematic reviews?
    1. Yes. You should undertake an Umbrella Review.
    2. No. Continue to question 6.
  6. Do you have a well formulated research question?
    1. No. Systematic reviews are conducted in an unbiased, reproducible way to provide evidence for practice and policymaking and to identify gaps in research. They require a well formulated research question.
    2. Yes. Continue to question 7.
  7. You should proceed with a Systematic Review. Continue to question 8.
  8. Will you use statistical methods to objectively evaluate, synthesize, and summarize your results?
    1. Yes. You should include Meta-Analysis of your results.
    2. No. A Meta-Analysis will not be needed.

What is a Systematic Review?

A Systematic Review is team based and is a means of identifying, evaluating and interpreting all available research relevant to a particular research question, or topic area, or phenomenon of interest.

It has:

  • 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 (e.g., evaluating risk of bias);
  • A systematic presentation, and synthesis, of the characteristics and findings of the included studies.

 

Protocol:
A priori review protocol should be created at the start of the review and registered on PROSPERO.     
Timeframe: Can take up to a year.
Team based:  Yes.
Question: Narrow question. May use PICO.
Sources and searches:      Needs to be exhaustive. May include Grey Literature.   
Appraisal: Critical and Rigorous
Selection: Based on inclusion/exclusion criteria.
Synthesis: Can be qualitative or Meta-Analysis.

Figure 1. Table of specifications for a Systematic Review.

 

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Image of the Sage Methods map for Systematic Review. Click the image to redirect to the live, interactive Sage methods map.

Figure 2. Sage Methods Map of Systematic Reviews. Click on the image above for more information about Systematic Reviews.

What is a Meta-Analysis?

A Meta-Analysis is a quantitative, formal, epidemiological study design used to systematically assess previous research studies to derive conclusions about that body of research. Outcomes from a Meta-Analysis may include a more precise estimate of the effect of treatment or risk factor for disease, or other outcomes, than any individual study contributing to the pooled analysis. The examination of variability or heterogeneity in study results is also a critical outcome. The benefits of meta-analysis include a consolidated and quantitative review of a large, and often complex, sometimes apparently conflicting, body of literature. 

Haidich, A. B. (2010) 'Meta-analysis in medical research', Hippokratia, 14(Suppl 1), pp. 29-37. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3049418/pdf/hippokratia-14-29.pdf
 

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An image of the Sage Methods Map for Meta-Analysis. Click on the image to redirect to the live, interactive Sage methods map for Meta-Analysis.

Figure 1. Sage Methods Map for Meta-Analysis. Click on the image above for more information on Meta-Analysis.

What is a Scoping Review?

Scoping Reviews are team based preliminary assessments of the potential size and scope of available research literature.  They aim to identify the nature and extent of research evidence (usually including ongoing research).

 

Protocol: A protocol should be created at the start of the review and registered.
Timeframe: 12+ months.
Team based:  Yes
Question: Answers broader and topic focused questions beyond those relating to the effectiveness of treatments or interventions.
Sources and searches:      Comprehensive search-may be limited by time/scope restraints, still aims to be thorough and repeatable of all literature.   
Appraisal: Optional. if you plan on appraising the literature a clear rationale and a description of the methods used should be given.
Selection: Based on inclusion/exclusion criteria, due to the iterative nature of a scoping review some changes may be necessary.
Synthesis: Tabular with some narrative.

Figure 1. Table of specifications for a Scoping Review.

 

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What is a Rapid Review?

A Rapid Review is team based and speeds up the Systematic Review process by omitting stages of the systematic review making it less rigorous.  

Rapid Reviews are best designed for: new or emerging research topics, updates of previous reviews, critical topics, to assess what is already known about a policy or practice using some Systematic Review methods.

 

Protocol: Develop a protocol that includes review questions, PICOS, and inclusion and exclusion criteria
Timeframe: ≤ 5 weeks (varies).
Team based:  Yes
Question: Narrow question, may use PICO.
Sources and searches:      Sources are limited due to time constraints of searching, however still uses transparent and reproducible search methods.   
Appraisal: Critical and rigorous but time limited.
Selection: Based on inclusion/exclusion criteria.
Synthesis: Synthesize evidence narratively. Standards for conducting a meta-analysis for a systematic review also apply to a Rapid Review. Only consider a meta-analysis if studies are similar enough to pool

Figure 1. Table of specifications for a Rapid Review.

 

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What is an Umbrella Review?

An Umbrella Review is team based and a Systematic Review and assessment of multiple existing Systematic Reviews and Meta-Analyses on a specific, shared research topic:

  • Umbrella Reviews were developed to deal with the increasing number of Systematic Reviews and Meta-Analyses in biomedical literature;

  • The validity of Umbrella Reviews depends on the coverage and quality of both the primary studies and the available Systematic Reviews and Meta-Analyses;

  • The key output of Umbrella Reviews is a systematic and standardised assessment of all the evidence on a broad but well defined research topic (eg, treatment effects of multiple interventions for a particular disease, or adjusted or unadjusted associations of multiple risk factors with a particular disease) based on published Systematic Reviews and Meta-Analyses.

Belbasis L, Bellou V, Ioannidis JPA Conducting umbrella reviews BMJ Medicine 2022;1:e000071. doi.org/10.1136/bmjmed-2021-000071

 

Protocol: The umbrella review should be preceded by an a priori, peer-reviewed protocol.
Timeframe: ≤ 1 year.           
Team based:  Yes.
Question: An umbrella review provides a summary of existing research syntheses related to a given topic or question.   
Sources and searches:      Comprehensive review of all Research Syntheses relevant to the review question.   
Appraisal: Critical and rigorous.
Selection: Based on inclusion/exclusion criteria.
Synthesis: Tabular with detailed description.

Figure 1. Table of specifications for an Umbrella Review.

 

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What is a Literature Review?

"A literature review is a written document that presents a logically argued case founded on a comprehensive understanding of the current state of knowledge about a topic of study. This case establishes a convincing thesis to answer the study's question." 

(Machi, L.A. & McEvoy, B.T. 2009, The literature review: six steps to success, p. 4)

A Literature Review:

  • Is a critical, in-depth evaluation of research already undertaken on a specific topic;
  • Allows you to demonstrate your ability to identify relevant information and to outline existing knowledge;
  • Identifies the gap in the research that your work will address and produce a rationale for your own research;
  • Is not a list of all previous research, but rather an assessment of the research.

For additional guidance, please refer to our more comprehensive Literature Review Guide.

 

Protocol: No protocol is included.
Timeframe: Varies.          
Team based:  No team, done by individuals.
Question: Not necessarily focused on a single question, but may describe an overview.    
Sources and searches:      Strategy not explicitly stated.
Appraisal: Appraisal criteria may or may not be mentioned.
Selection: Selection criteria may or may not be identified.
Synthesis: Up to the discretion of author.

Figure 1. Table of specifications for a Literature Review.

 

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