Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology
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Neuropsychopharmacology · Aug 1990
Comparative StudyTests of one-sided versus two-sided hypotheses in placebo-controlled clinical trials.
The p value associated with a test of significance is supposed to represent the probability of observed results given that the null hypothesis is actually true. In evaluating the efficacy of a new drug against placebo, regulatory considerations focus on superiority of the new drug over placebo. ⋯ Thus, the only probability of concern is the probability that apparent superiority of drug over placebo is a chance finding, and that is the probability associated with a one-tailed test. Where multiple studies must be evaluated with regard to the regulatory decision, meta-analytic considerations further support the relevance of one-sided p values.