In this article, I discuss measures of effect size for two-group comparisons where data are not appropriately analyzed by least-squares methods. The Mann–Whitney test calculates a statistic that is a very useful measure of effect size, particularly suited to situations in which differences are...

Somers' D is an asymmetric measure of association between two variables, which plays a central role as a parameter behind rank or nonparametric statistical methods. Given predictor variable X and outcome variable Y, we may estimate D(YX) as a measure of the effect of X on Y, or we may estimate...

So-called "nonparametric" statistical methods are often in fact based on population parameters, which can be estimated (with confidence limits) using the corresponding sample statistics. This article reviews the uses of three such parameters, namely Kendall's tau, Somers' D and the...