Research studies in diagnostic radiology often compare the diagnostic abilities of two imaging techniques. The "power" of such studies is the probability that they will detect a difference in abilities of a certain amount when, indeed, such a difference does exist. This article outlines several strategies that can be used to assess and improve the power of radiologic diagnostic studies. These strategies include selection of cases and controls, matching, use of one-tailed tests, selection of significance level, and choice of sample size.