Meta-Analytic Procedures for Combining Studies With Multiple Effect Sizes

Abstract

In this article we present a general set of meta-analytic procedures for combining and comparing research results from studies yielding multiple effect sizes based on multiple dependent variables. These require, in addition to the individual effect sizes or significance levels, only the degrees of freedom in the study and the typical intercorrelation among the variables. Older methods are reviewed, and a new method is presented for obtaining a single summary effect size estimate from multiple effect sizes. Significance testing of this summary effect size estimate is described. Procedures for computing the effect size for a contrast, and its significance level, among the multiple effect sizes of a single study are also described. Finally, methods for dealing with problems of heterogeneous intercorrelations among the dependent variables are presented.