The use of one-sided tests in drug trials: an FDA advisory committee member's perspective.

The use of one-sided or two-sided tests in drug trials to evaluate new compounds is considered. For drugs that may be tested against placebos, with two positive trials required (as in the United States), it is argued that from both a regulatory and pharmaceutical industry perspective, one-sided tests at the 0.05 significance level are appropriate. In situations where only one trial against placebo may be done (for example, survival trials), one-sided tests at the 0.025 level are appropriate in many cases. For active control trials it is argued that two-sided tests are usually appropriate.