p-value adjustments for subgroup analyses.

The analysis of data from clinical trials often includes subgroup analyses, which are performed to examine the treatment effect within various sets of patients based on baseline and/or demographic variables. The goals of these analyses are to establish the consistency of the results across the subgroups and to identify important prognostic factors. The p-values for such analyses are usually presented without any adjustment for the multiple analyses: This approach has been criticized because of the possibility of misleading false positives. Conservative approaches have been proposed to resolve this problem; however, these approaches are usually so conservative that significant results are rarely observed after adjustment. Here an approximate technique for use when the variable of interest has a normal distribution is presented.