Screening and diagnostic tests are common in the fields of psychology, medicine, and education. Often there are several competing tests, and decisions must be made about the relative accuracy of those tests. This article describes a general measure that can be used for both continuous and dichotomous outcome measures. It is the standardized distance between the means of the 2 populations. For continuous measures, it is the effect size measure. For dichotomous measures, it is proportional to the logarithm of the odds of the sensitivity plus the logarithm of the odds of the specificity. The measure is easily computed for both kinds of outcomes. Properties of this measure are discussed, and examples are given. Ths use of this measure to compare the average performance of different tests is described.