Colloquy: Should Familywise Alpha Be Adjusted?.

Abstract

Type I error is a risk undertaken whenever significance tests are conducted, and the chances of committing a Type I error increase as the number of significance tests increases. But adjusting the alpha level because of the number of tests conducted in a given study has no principled basis, commits one to absurd beliefs and practices, and reduces statistical power. The practice of requiring or employing such adjustments should be abandoned.