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Definitions and types of reviews

Understanding what type of reviews exist and the aim of the review type will help you determine what type of review you should conduct. There are 14 types of reviews, including systematic reviews.

What is a systematic review?

A systematic review gathers evidence that aligns with specific eligibility criteria to answer a specific research question. It aims to minimize bias by using explicit and systematic methodology that have been determined using a protocol.

Systematic reviews often include:

  • An extensive search of evidence to find relevant studies,
  • Inclusion and exclusion criteria,
  • A validity assessment of the included studies, and
  • Recommendations for future practice

Source: Chandler J, Cumpston M, Thomas J, Higgins JPT, Deeks JJ, Clarke MJ. Chapter I: Introduction. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.3 (updated February 2022). Cochrane, 2022. Available from www.training.cochrane.org/handbook.

Other Review Types

In addition to systematic reviews, there are other types of knowledge synthesis projects that you can conduct. These other types of reviews include, but are not limited to:

  • Scoping Reviews aim to identify the type and the extent of the research that currently exists on a topic. They provide researchers a way of assessing the size and scope of existing literature.
  • Meta-Analysis is a technique that consists of conducting a comprehensive search of existing research and combine the numerical results of existing studies in order to provide a concise statistical summary of findings.
  • Narrative Reviews (also referred to as literature reviews) aim to examine the existing/current literature that exists on a particular research area. They may or may not be comprehensive.
  • Umbrella Reviews are reviews of systematic reviews or meta-analyses; they do not rely on primary sources. They will often put the findings of multiple reviews in one document and focus on a broad research question or problem.

For more detailed information on review types, refer to A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.

Not sure what review is right for you? Try the Right Review tool, provided by the Knowledge Translation Program, which is designed to help you determine which type of review would be best for your knowledge synthesis project.

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Planning your review / knowledge synthesis project

Before you begin, ensure that you have the time and people to conduct a knowledge synthesis project.

  • Time: Depending on the size of your review and the scope of your question, a systematic or scoping review may take a year or more to complete. If you need to complete a project within an academic semester, a scoping or systematic review may not be the best choice.
  • Research team: At minimum, your research team should consist of two people to independently screen your results. Depending on the size of your review, it may be advisable to look for more team members to serve as additional screeners (and tiebreakers in the case of disagreement), subject matter experts, a statistician and a search specialist.

The research question

It is important to have a precise and well-defined question prior to starting your review. This will prevent bias by preventing you from re-framing your question based on the studies you find in your search. You will use your question to inform your search strategy and study selection criteria.

PICO — population, intervention, comparison, outcome — is a popular framework used to help construct your research questions.

For other frameworks, see:

Inclusion and exclusion criteria

Your selection criteria place limits on your review and are determined before you begin searching. These criteria are informed by your Research Question and can be used to help shape your search. Inclusion and exclusion criteria can inadvertently introduce bias, so it is important to understand and be able to explain your rationale for your selection criteria.

Your criteria should be well defined so they can be applied consistently by all screeners. You are encouraged to pilot your criteria to ensure they are being applied as intended during screening. At this point, you should also develop a strategy for how screening disagreements will be resolved.

The University of Melbourne guide has a chart of common inclusion and exclusion criteria with brief descriptions, which may be helpful when determining criteria for your review.

Review protocol

The protocol is your research plan. It lays out your review rationale and question, methods (including search and study inclusion/exclusion criteria), and your plan for data analysis.

Protocols define your process to ensure a systematic approach and can help you stay on track with your review. As well, since systematic reviews and other knowledge synthesis projects can take a long time to complete, searching protocol registries before you begin and registering your protocol helps prevent duplication and wasted time.

Protocol databases

Some journals, like BMC Systematic Reviews, publish review protocols. However, there are also registries that allow you search protocols and upload your own.

  • PROSPERO is a database and registry of protocols. They only accept protocols for systematic reviews, rapid reviews and umbrella reviews, in health topics or topics with a health-related outcome.
  • OSF: Open Science Framework is an open-source collaboration software that allows you to publish your review protocols along with data files. If you are conducting a scoping review or a non-health related review, OSF is a good place for your protocol.

Resources for writing protocols

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Resources

Access the resources listed below to learn more about systematic reviews, their process, and examples of studies using systematic review methods.

Books, manuals and methodology guides

Systematic reviews and meta-analysis

Scoping reviews

Discipline specific

Free courses, tutorials, and videos

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