Clinical Trials

❘❙❚■ Chapter 29 | Multiplicityof 0.05. By performing such a correction, the probability that one or more of thetests will produce a statistically significant result if the null hypothesis is trueis approximately 0.05, maintaining the traditional significance level.An example of this is seen in a multicenter trial of hormonal emergencycontraception for healthy women [6]. One part of the outcome assessmentincluded testing for differences in the occurrence of one or more side-effects(nausea, changes in menstrual bleeding, headache, etc). In total there were10 side-effects that were potentially due to emergency contraception, giving anadjusted significance level of 0.005. After Bonferroni correction, mifepristone wasstill significantly associated with less and delayed menstrual bleeding compared tolevonorgestrel because the P-value obtained for this test was