"Evidence synthesis is 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. The transparent methodology encompasses how studies are identified, selected, appraised, analyzed, and the strength of the evidence assessed to answer the questioned posed."
See also Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information & Libraries Journal, 26(2), 91-108.
Various approaches can be used to organize the review.
Adapted from Cronin, P. BJN, 2008, Vol 17, No 1 p.42