When more than one statistical test is performed in analysing the data from a clinical study, some statisticians and journal editors demand that a more stringent criterion be used for “statistical significance” than the conventional P<0.05.

^{1}Many well meaning researchers, eager for methodological rigour, comply without fully grasping what is at stake. Recently, adjustments for multiple tests (or Bonferroni adjustments) have found their way into introductory texts on medical statistics, which has increased their apparent legitimacy.^{2}^{,3}This paper advances the view, widely held by epidemiologists, that Bonferroni adjustments are, at best, unnecessary and, at worst, deleterious to sound statistical inference.^{4}^{,5}Summary points

- Adjusting statistical significance for the number of tests that have been performed on study data—the Bonferroni method—creates more problems than it solves
- The Bonferroni method is concerned with the general null hypothesis (that all null hypotheses are true simultaneously), which is rarely of interest or use to researchers
- The main weakness is that the interpretation of a finding depends on the number of other tests performed
- The likelihood of type II errors is also increased, so that truly important differences are deemed non-significant
- Simply describing what tests of significance have been performed, and why, is generally the best way of dealing with multiple comparisons