Abstract
This article describes a multivariate effect size measure useful in social and behavioral research, which complements existing descriptive indicators of group differences. The measure reflects probabilistic aspects of the disparity of two multivariate distributions, and its interpretation does not require advanced training in statistics. Estimation of the discussed effect size indicator is illustrated on data from a two-group cognitive intervention study (Baltes, Dittmann-Kohli, & Kliegl, 1986).