PROBABILITY OF THE SUPERIOR OUTCOME OF ONE TREATMENT OVER ANOTHER

An intuitively appealing indicator of magnitude of effect in applied research is an estimate of the probability of the superior outcome of one treatment over another. Parametric and nonparametric estimates are discussed, as is a meta-analytic estimate. Estimates from values of t, the point-biserial correlation, and standardized effect size are presented. A new perspective on J. Cohen's (1988) standards for small, medium, and large effect sizes is provided. Psychologists who are conducting applied primary research or meta-analyses are urged to include such estimation in their reports.