Overview of evidence synthesis types and modes

Health-care decisions should be based on the best available evidence. To bring together findings from many studies, researchers use evidence synthesis-structured methods that summarize what is known on a topic. Because health questions differ, various types of evidence syntheses exist, each designed for specific needs. This article explains the aims and characteristics of the most common types of evidence synthesis: systematic reviews, overviews of reviews, qualitative evidence syntheses, mixed methods reviews, and 'big picture reviews' (scoping reviews, mapping reviews, and evidence gap maps). We also describe two ways evidence syntheses can be carried out: rapid reviews (done quickly to support urgent decisions) and living reviews (regularly updated as new evidence becomes available). Understanding the different approaches helps clinicians, patients, and policymakers select the right type of review for their health questions. This ensures that decisions are guided by evidence that is both reliable and appropriate for the situation.