The nature of the evidence: A synthesis of meta-analyses

This chapter outlines the methodology relating to the evidence used in the remainder of this book. The fundamental unit of analysis is 800+ meta-analyses and how the major results from these studies can be placed along a single continuum. The chapter then outlines some of the problems of meta-analyses, discusses some of the previous attempts to synthesize meta-analyses, and then introduces some of the major overall findings from the synthesis of the 800+ meta-analyses.