Comparing effect sizes of independent studies.

Abstract

This article presents a general set of procedures for comparing the effect sizes of two or more independent studies. The procedures include a method for calculating the approximate significance level for the heterogeneity of effect sizes of studies and a method for calculating the approximate significance level of a contrast among the effect sizes. Although the focus is on effect size as measured by the standardized difference between the means (d) defined as (Mi — M-^/S,\nthe procedures can be applied to any measure of effect size having an estimated variance. This extension is illustrated with effect size measured by the difference between proportions.

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