Approaching the body of evidence: Key concepts of Overviews.

The increasing production of primary research and literature reviews in the last decades has made it necessary to develop a new methodological design to synthesize the evidence: the overviews. An overview is a type of evidence synthesis that uses systematic reviews as the unit of analysis, with the aim of extracting and analyzing the results for a new or broader research question, helping the shared decision-making processes. The aim of this article is to introduce the reader to this type of evidence summaries, highlighting the differences between overviews and other types of synthesis, the unique methodological aspects of overviews, and future challenges. This is the twelfth article from a collaborative methodological series of narrative reviews about biostatistics and clinical epidemiology.