Evidence Synthesis International describes Evidence Synthesis this way...

"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.  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.

Evidence syntheses methods have been applied to a diverse and growing number of areas. Applications, include: education, crime and justice, international development, health care delivery, health technology assessment, veterinary medicine, pre-clinical drug development and toxicology, food safety, and environmental conservation. As equally diverse as the applications are the organizations that conduct, commission, and utilize the evidence synthesis."

Evidence Synthesis International. (n.d.). What is Evidence Synthesis. Retrieved January 25, 2021, from https://evidencesynthesis.org/what-is-evidence-synthesis/

Evidence synthesis refers to any method of identifying, selecting, and combining results from multiple studies.  The following are some types of evidence synthesis.

Systematic Review

• Exhaustive review of primary evidence on a clearly formulated question.
• Methods must be transparent, reproducible and follow an established protocol.

Literature (Narrative) Review

• A broad term referring to reviews with a wide scope and non-standardized methodology. 
• Search strategies, comprehensiveness, and time range covered will vary and do not follow an established protocol.

​Scoping Review or Evidence Map

• Systematically and transparently collect and categorize existing evidence on a broad question of policy or management importance.
• Seeks to identify research gaps and opportunities for evidence synthesis rather than searching for the effect of an intervention. 
• May critically evaluate existing evidence, but does not attempt to synthesize the results in the way a systematic review would. (see EE Journal and CIFOR)
• May take longer than a systematic review.
• See Arksey and O'Malley (2005) for methodological guidance.

​Rapid Review

• Applies Systematic Review methodology within a time-constrained setting.
• Employs methodological "shortcuts" (limiting search terms for example) at the risk of introducing bias.
• Useful for addressing issues needing quick decisions, such as developing policy recommendations.
• See Evidence Summaries: The Evolution of a Rapid Review Approach

Umbrella Review

• Reviews other systematic reviews on a topic. 
• Often defines a broader question than is typical of a traditional systematic review.
• Most useful when there are competing interventions to consider.

Meta-analysis

• Statistical technique for combining the findings from disparate quantitative studies.
• Uses statistical methods to objectively evaluate, synthesize, and summarize results.
• May be conducted independently or as part of a systematic review.
   

The above was adapted from Cornell University LIbrary's A Guide to Evidence Synthesis: Types of Evidence Synthesis, https://guides.library.cornell.edu/evidence-synthesis/types

Follow the links below to tools which will help you to determine which evidence synthesis method will work for you.