ABSTRACT
Meta-analysis was defined by the American Heritage Dictionary of the English Language (2000) as ‘‘the process or technique of synthesizing research results by using various statistical methods to retrieve, select, and combine results from previous separate but related studies.’’ The term metaanalysis was first used by Glass in 1976. Later he and his associate used the method to statistically integrate the results of 375 psychotherapy studies to show the benefits of psychotherapy to patients’ mental health (Smith and Glass, 1977).
