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Systematic Reviews and Evidence Syntheses: Types of Evidence Syntheses

A guide to the methodology of and resources for Systematic Reviews

Common forms of evidence synthesis

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), (2nd 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

Systematic reviews: one of the most common types of evidence syntheses

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".

  • 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 6.0 (updated August 2019). Cochrane, 2019. Available from www.training.cochrane.org/handbook.

Is a systematic review a thorough or robust literature review?

No. A systematic review has different steps in its methodology than a literature or narrative review does. A systematic review can also be considered a type of primary research whereas a traditional literature or narrative review article is not. 

A systematic review also has specific research team requirements including a minimum of two independent subject experts to complete the screening portions of the systematic review.

Additional information about systematic review may be found in SAGE Research Methods. Search for "systematic review" for definitions and other supporting resources. 

Systematic reviews are only one type of evidence syntheses. See the page Types of Evidence Syntheses for more information about other types.

What does a systematic review contain?

Systematic review methodology was developed by Cochrane and is still the gold standard today. It sets a "highly structured, transparent and reproducible methodology" (Chandler and Hopewell 2013). This involves:

  1. the a priori specification of a research question;
  2. clarity on the scope of the review and which studies are eligible for inclusion;
  3. making every effort to find all relevant research and to ensure that issues of bias in included studies are accounted for;
  4. analyzing the included studies in order to draw conclusions based on all the identified research in an impartial and objective way (Lasserson et al 2019).

Each of these items represents a complex and important piece of a systematic review. For more information about completing these items, please see the recommended additional readings and/or reach out to one of our librarians. 

  • Chandler J, Hopewell S. Cochrane methods – twenty years experience in developing systematic review methods. Systematic Reviews 2013; 2: 76.

  • Lasserson TJ, Thomas J, Higgins JPT. Chapter 1: Starting a review. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.0 (updated July 2019). Cochrane, 2019. Available from www.training.cochrane.org/handbook.

Am I doing a systematic review?

Check out this flow chart from Cornell University to see what type of review most closely matches your project: https://www.library.cornell.edu/sites/default/files/SystematicReview_DecisionTreeMethodologies_v3.pdf

Additional Reading on Systematic Reviews and Other Review Types

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.

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