"Evidence synthesis uses formal, explicit, and rigorous methods to bring together the findings of research already completed, to provide an account of the totality of what is known from that pre-existing research." 1

A systematic review is a type of evidence synthesis that evaluates the "evidence on a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant primary research, and to extract and analyze data from the studies that are included in the review." The methods used must be reproducible and transparent. 2

Evidence synthesis requires:

• A clearly formed question
• Transparent and reproducible methods of identifying, categorizing, and analyzing the literature
• A comprehensive search of the literature 
• Explicit inclusion and exclusion criteria
• Efforts to reduce bias in study selection and reporting

See our Library Guide on Evidence Synthesis (Systematic Reviews) for a comprehensive overview of this type of research.

References:

1. Gough D, Davies P, Jamtvedt G, et al. Evidence Synthesis International (ESI): Position Statement. Systematic Reviews. 2020;9(1):155. doi:10.1186/s13643-020-01415-5

2. Wright RW, Brand RA, Dunn W, Spindler KP. How to write a systematic review. Clin Orthop Relat Res. 2007;455:23-29. doi:10.1097/BLO.0b013e31802c9098