Abstract
We introduce the binomial effect size display (BESD), which is useful because it is (a) easily understood by researchers, students, and lay persons; (b) widely applicable; and (c) conveniently computed. The BESD displays the change in success rate (e.g., survival rate, improvement rate, etc.) attributable to a new treatment procedure. For example, an r of .32, the average size of the effect of psychotherapy, is said to account for only 10% of the variance; however, the BESD shows that this proportion of variance accounted for is equivalent to increasing the success rate from 34% to 66%, which would mean, for example, reducing an illness rate or a death rate from 66% to 34%. Traditionally, behavioral researchers have concentrated on reporting significance levels of experimental effects. Recent years, however, have shown a welcome increase in emphasis on reporting the magnitude of experimental effects obtained (Cohen, 1977; Fleiss, 1969; Friedman, 1968, Glass, Note 1, Hays, 1973; Rosenthal, 1978; Rosenthal & Rubin, 1978; Smith & Glass, 1977).
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