Basic statistical testing, including interim analysis.

Clinical trials, due to the randomization process, require statistical methods for testing key hypotheses that are straightforward and involve simple comparisons of group proportions or group means. Differences between group proportions are tested using a chi 2 statistic or a Fisher's exact test. Differences between group means are tested using a two-sample t statistic. When there are more than two groups, the F statistic is calculated. When ordinal data or data not normally distributed are analyzed, nonparametric testing is performed. A critical decision prior to analysis is the choice of the endpoint, which must be clearly defined and consistently applied. Monitoring a clinical trial is important, and may lead to interim analysis. This should be done by independent study monitors. Interim results play an important role in analyzing clinical trials; however, they create problems due to multiple testing. An early stoppage rule is frequently applied when independent interim results are obtained. The statistical methods for interim analysis are discussed.