When to use the Bonferroni correction

Abstract Purpose The B onferroni correction adjusts probability ( p ) values because of the increased risk of a type I error when making multiple statistical tests. The routine use of this test has been criticised as deleterious to sound statistical judgment, testing the wrong hypothesis, and reducing the chance of a type I error but at the expense of a type II error; yet it remains popular in ophthalmic research. The purpose of this article was to survey the use of the B onferroni correction in research articles published in three optometric journals, viz. O phthalmic & P hysiological O ptics , O ptometry & V ision S cience , and C linical & E xperimental O ptometry , and to provide advice to authors contemplating multiple testing. Recent findings Some authors ignored the problem of multiple testing while others used the method uncritically with no rationale or discussion. A variety of methods of correcting p values were employed, the B onferroni method being the single most popular. B onferroni was used in a variety of circumstances, most commonly to correct the experiment‐wise error rate when using multiple ‘ t ’ tests or as a post‐hoc procedure to correct the family‐wise error rate following analysis of variance ( anova ). Some studies quoted adjusted p values incorrectly or gave an erroneous rationale. Summary Whether or not to use the B onferroni correction depends on the circumstances of the study. It should not be used routinely and should be considered if: (1) a single test of the ‘universal null hypothesis’ ( H o ) that all tests are not significant is required, (2) it is imperative to avoid a type I error, and (3) a large number of tests are carried out without preplanned hypotheses.