Meta-analysis at middle age: a personal history. 
The 40-year history of meta-analysis is traced from the vantage point of one of its originators.  Research syntheses leading to the first examples of meta-analysis are identified.  Early meta-analyses of the literature on psychotherapy outcomes and school class size are recounted.  The influence on the development of meta-analysis of several statisticians and psychologists is described.  Finally, some directions for future development of research synthesis methods are suggested.