To increase power in randomized clinical trials without increasing sample size.

The power of a randomized clinical trial (RCT) depends on two factors: sample size and effect size. Most psychiatric research design strategies focus on increasing sample size, despite major problems in recruiting large numbers of subjects or funding such costly studies. It is possible to increase power in RCTs in a variety of ways without increasing sample size, in essence by increasing effect size by decreasing within-group variance. Such strategies are presented and discussed.