Sample size {14}
death
REGRESSION, EVENT
Sample size calculation is based on the rate of the primary endpoint (IH rate) within 24 months after surgery. Based on the assumption that the percentage of patients developing an IH in the control group is 30% (4–7), we hypothesise a reduction to 15% in the intervention arm (conservative reduction rate below that reported in the above-mentioned trials). Consequently, a sample size per group of 121 patients is needed for the group comparison by the chi-squared test to achieve 80% power in detecting this difference in IH rate at a two-sided level of significance of 5%. It is assumed that using a logistic regression model adjusting for IH risk (low-risk vs. high-risk patients: BMI ≥ 27) and including centre as a random effect in the primary analysis will lead to less unexplained variance and thus to an increased power.The intercurrent event re-laparotomy affecting the loop ileostomy closure site and death without prior observation of IH are expected to be very rare, with just a few patients each. Based on previous trials, to account for the loss of information, a rate of 20% of dropouts, loss to FU and relevant ICEs (handled with the hypothetical strategy) is considered. Therefore, a total of 304 patients (152 per group) will be randomised. The other ICEs are ignored in the primary estimand and not accounted for in the sample size calculation. Calculation was performed using PASS 16.0.12. Only high-volume trial sites committing to include at least 10 patients per year will be chosen as trial sites.