Current thinking on validity suggests that educational institutions and individuals should evaluate their uses of test scores in the context of their fundamental goals. Regression coefficients and other traditional criterion-related validity statistics provide relevant information, but often do not, by themselves, address the fundamental reasons for using test scores. Formal decision theory models provide a logically rigorous way to do this, but they are difficult to implement in practice. This article considers a simplification of formal decision theory models, in which one estimates the proportion of examinees for whom positive outcomes result from a use of test scores. For uses involving selection, the proportion of examinees with positive outcomes can be calculated by applying traditional regression coefficients to the marginal distribution of scores in the unselected population. The incremental usefulness of using a particular variable can be judged by comparing its proportion to that associated with no selection and to that associated with using another variable, either alone or jointly. Examples, related to college admission and retention, are given to illustrate these ideas.