Multivariate misgivings: is D a valid measure of group and sex differences?

Abstract

In the study of group and sex differences in multivariate domains such as personality and aggression, univariate effect sizes may underestimate the extent to which groups differ from one another. When multivariate effect sizes such as Mahalanobis D are employed, sex differences are often found to be considerably larger than commonly assumed. In this paper, I review and discuss recent criticism concerning the validity of D as an effect size in psychological research. I conclude that the main arguments against D are incorrect, logically inconsistent, or easily answered on methodological grounds. When correctly employed and interpreted, D provides a valid, convenient measure of group and sex differences in multivariate domains.