Systematic Reviews and Evidence Syntheses : Types of Evidence Syntheses

Given the variety of evidence synthesis methodologies, it is not always easy to determine which methodology is best for your research project. Luckily, folks in the evidence synthesis community have built tools to help in this process.

Dr. Andrea Tricco and the Knowledge Translation Program developed the Right Review tool, which is designed to provide guidance and supporting material to reviewers on methods for the conduct and reporting of knowledge synthesis.

In addition, folks at Cornell University Libraries developed a decision tree for evidence synthesis methodologies.

Please don't hesitate to reach out if you would appreciate personalized help in determining which will be the best fit for your needs and goals.

Literature Review: This is a traditional review article, sometimes known as a narrative review.

• "Generic term: published materials that provide examination of recent or current literature. Can cover wide range of subjects at various levels of completeness and comprehensiveness. May include research findings map" (Grant, 2009)

Systematic Review: One of the most well-known types of evidence synthesis.

• According to the Cochrane Handbook, "systematic reviews seek to collate evidence that fits pre-specified eligibility criteria in order to answer a specific research question. They aim to minimize bias by using explicit, systematic methods documented in advance with a protocol".

Rapid Review: A rapid review follows the systematic review format but with a less intensive search process requiring a thorough search of one database rather than a minimum of three. 

• "Assessment of what is already known about a policy or practice issue, by using systematic review methods to search and critically appraise existing research" (Grant, 2009)

Systematized Review: A review type that does not meet the methodology requirements for a Systematic Review (such as two reviewers), but still follows similar methodology.

• "Systematized reviews attempt to include one or more elements of the systematic review process while stopping short of claiming that the resultant output is a systematic review. Systematized reviews are typically conducted as a postgraduate student assignment, in recognition that they are not able to draw upon the resources required for a full systematic review (such as two reviewers)." (Grant, 2009)

Scoping Review: A scoping review is a broader review to determine a general idea of what has been published on a topic.

• "Preliminary assessment of potential size and scope of available research literature. Aims to identify nature and extent of research evidence (usually including ongoing research)" (Grant, 2009)

Umbrella Review: Commonly defined as a 'systematic review of systematic reviews'. 

• "Specifically refers to review compiling evidence from multiple reviews into one accessible and usable document. Focuses on broad condition or problem for which there are competing interventions and highlights reviews that address these interventions and their results" (Grant, 2009)

Realist Review: Also known as "realist synthesis", this is a form of evidence synthesis designed for complex policy interventions.

• "Answers the question “What works for whom under what circumstances?” rather than “What works?”. Specifically, it seeks to unpack the mechanism of how complex programmes work (or why they fail) in particular contexts and settings" (Booth, 2016).

Integrative Review:

• A well-done integrative review is conducted with the same rigor as a systematic review and is one of the broadest types of research review methods.  Integrative reviews allow for the “simultaneous inclusion of experimental and non-experimental research in order to more fully understand a phenomenon of concern. Integrated reviews may also combine data from the theoretical as well as empirical literature. In addition, integrative reviews incorporate a wide range of purposes: to define concepts, to review theories, to review evidence, and to analyze methodological issues of a particular topic” (Broome 1993).

Booth, A. (2016). Searching for qualitative research for inclusion in systematic reviews: A structured methodological review. Systematic Reviews, 5, 74. https://doi-org.ezproxy.neu.edu/10.1186/s13643-016-0249-x

Broome, M.E., (1993). Integrative literature reviews for the development of concepts. In B.L. Rodgers & K.A. Knafl (Eds.), Concept Development in Nursing (231-250), (2^nd ed.). Philadelphia: W.B. Saunders Co.

Grant, M. J., & Booth, A. (2009). A typology of reviews: An analysis of 14 review types and associated methodologies. Health Information and Libraries Journal, 26(2), 91–108. https://doi.org/10.1111/j.1471-1842.2009.00848.x

Recommended Texts on Systematic Reviews:

Cochrane Handbook for Systematic Reviews of Interventions

• Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.0 (updated July 2019). Cochrane, 2019. Available from www.training.cochrane.org/handbook.

Finding What Works in Health Care: Standards for Systematic Reviews

• Institute of Medicine (US) Committee on Standards for Systematic Reviews of Comparative Effectiveness Research; Eden J, Levit L, Berg A, et al., editors. Finding What Works in Health Care: Standards for Systematic Reviews. Washington (DC): National Academies Press (US); 2011. Available from: https://www.ncbi.nlm.nih.gov/books/NBK209518/ doi: 10.17226/13059

Articles on Different Types of Reviews:

Meeting the review family: Exploring review types and associated information retrieval requirements

• Sutton, A., Clowes, M., Preston, L., & Booth, A. (2019). Meeting the review family: Exploring review types and associated information retrieval requirements. Health Information & Libraries Journal, 36(3), 202–222. https://doi.org/10.1111/hir.12276

Evidence Summaries: The Evolution of a Rapid Review Approach 

• Khangura, Sara, Kristin Konnyu, Rob Cushman, Jeremy Grimshaw, and David Moher. (2012). Evidence Summaries: The Evolution of a Rapid Review Approach. Systematic Reviews, 1(1), 10. https://doi.org/10.1186/2046-4053-1-10.