ON MAKING MULTIPLE COMPARISONS IN CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY

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Abstract
1. It is a central thesis of this review that in clinical and experimental pharmacology and physiology the goal of statistical analysis should be to minimize the risk of making any false–positive inferences from the results of an experiment (experimentwise Type I error). 2. It is common in clinical and experimental pharmacology and physiology for the effects of several treatments to be tested within a single experiment. Specific intercomparisons of these several effects, made in a pairwise or more complex fashion, inflates the risk of making false–positive inferences unless special statistical procedures are used. 3. A number of multiple comparison procedures is described and their ability to control experimentwise Type I error is evaluated critically. 4. When only a few (< 5) of all possible pairwise or more complex comparisons are made between treatment groups, the Dunn-Šdák procedure provides maximum protection against excessive experimentwise Type I error and is very convenient to use. 5. When a control group is compared with all other treatment groups in a pairwise fashion, especially when the number of groups is large, the Dunnett procedure is more powerful than the Dunn-Šidák. 6. If investigators insist on making all possible pairwise comparisons among treatment groups, the Tukey-Kramer procedure provides maximum protection against false-positive inferences but inflates the Type II error rate. If it is especially important to avoid Type II error then the more complicated, stepwise procedures of the Ryan-Peritz-Welsch variety should be considered.

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