2.5 Sample size calculation and statistical methods
REMISSION
A two-group chi-squared test with a 5% two-sided significance level had 80% power to detect a difference between a group 1 proportion, πDescriptive statistics were described as proportions with percentages or as means with standard deviations [SD] unless stated otherwise. Results were analysed according to an intention-to-treat principle, including all patients who received at least one dose of mercaptopurine or placebo. Participants who discontinued study treatment before week 52 or were lost to follow-up were considered non-responders [non-responder imputation]. Proportions were compared with a chi-square or Fischer’s exact test, if appropriate. To reduce the risk for multiple testing on this cohort, a hierarchical testing order was applied to a limited number of endpoints. If a test resulted in a significant result, the subsequent comparison could be performed. The hierarchical order was [I] combined clinical remission and endoscopic improvement, [II] endoscopic improvement, [III] clinical remission and [IV] histological remission. Other endpoints were presented as proportions without statistical comparisons. Unpaired continuous variables were non-parametrically compared with the Mann–Whitney U test, and the Wilcoxon signed-rank test was used for paired non-parametric comparisons. A 