The article “Meta-Analysis of Psychotherapy Outcome Studies,” written by Mary Lee Smith and Gene Glass and published in American Psychologist in 1977, initiated the use of meta-analysis as a statistical tool capable of summarizing the results of numerous studies addressing a single topic. In meta-analysis, individual research studies are identified according to established criteria and treated as a population, with results from each study subjected to coding and entered into a database, where they are statistically analyzed. Smith and Glass pioneered the application of meta-analysis in research related to psychological treatment and education. Their work is considered a major contribution to the scientific literature on psychotherapy and has spurred hundreds of other meta-analytic studies since its publication.