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Evidence Synthesis: Evidence Synthesis Approaches

Evidence Synthesis is a broad term used to describe several synthesis review methodologies, most familiar may be systematic reviews and meta-analyses.

Map of review methodologies  

1) Traditional Reviews sometimes called Narrative Reviews refer to the typical literature review approach which does not require adherence to a specific process, set of reporting guidelines and typically methods for including and excluding material is unclear.

2) Evidence Synthesis is defined by Evidence Synthesis International as...

...the interpretation of individual studies within the context of global knowledge for a given topic. These syntheses provide a rigorous and transparent knowledge base for translating research in decisions. As such, evidence syntheses can be thought of as the basic unit of knowledge used in tools such a policy brief or clinical practice guideline. In other words, evidence syntheses are the “evidence-base” in evidence-based policy, or evidence-based medicine etc. Essential to all evidence syntheses is the use of explicit and transparent methodology in the formation of the questions they address. 

3) Systematic Reviews aim to synthesize primary evidence as a means to answer a specific research question(s).

4) A meta-Analysis is a statistical approach to combining effect sizes from several studies. Meta-analyses should only be pursued if appropriate. Though a systematic review can be conducted without a meta-analysis, a meta-analysis should always be accompanied by a systematic review

5) Scoping and/or Mapping Reviews aim to illustrate the landscape of primary evidence and are most appropriate for broader research questions.

6) Review of Reviews or Overviews aim to synthesize findings from other reviews. This approach is only appropriate for topics on which several reviews have already been undertaken. Umbrella Reviews are a type of review of review that synthesizes only one type of review (e.g., an umbrella review of systematic reviews).

7) The modifier 'Restricted' or 'Rapid' is applied to one of the above review approaches when there is a serious limitation (e.g., not having a full team, lack of access for comprehensive search, no critical appraisal for a systematic review)

8) The modifier 'Living' is applied to one of the above approaches (most often systematic reviews and meta-analyses) that are intentionally ingesting new evidence and adjusting results on an ongoing basis

9) Qualitative synthesis loosely describes the process of synthesizing evidence. Examples of qualitative synthesis methods include meta-ethnography or framework synthesis. These approaches can be applied in all review types. In this context, it can help to think of, for example, the systematic or scoping review as a process that leads up to the synthesis.


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Overviews of review types

These are not the only evidence synthesis review approaches to choose from -- see the overviews below to explore other options!


Bouck, Z., Straus, S.E., Tricco, A.C. (2022). Systematic Versus Rapid Versus Scoping Reviews. In: Evangelou, E., Veroniki, A.A. (eds) Meta-Research. Methods in Molecular Biology, vol 2345. Humana, New York, NY.

Munn, Z., Peters, M.D.J., Stern, C. et al. Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Med Res Methodol 18, 143 (2018). 

Plüddemann A, Aronson JK, Onakpoya I, et al Redefining rapid reviews: a flexible framework for restricted systematic reviews BMJ Evidence-Based Medicine 2018;23:201-203.