Multiple comparisons in over-the-counter drug clinical trials with both positive and placebo controls

Evaluations of the efficacy of over-the-counter drugs using ANOVA techniques often misuse multiple comparison procedures. Studies that involve both a placebo control and established drugs as positive controls are especially prone to these problems. The most common mistake involves using a procedure which does not control the experimentwise type I error rate, usually the Duncan procedure or some version of multiple t tests. These procedures control comparisonwise type I error rate, but lack the important experimentwise error control. The purpose of this paper is to clarify the issues involved in performing ANOVA followed by a multiple comparison procedure for over-the-counter drug studies involving both placebo and positive controls.