Sample size calculations
stoma
The sample size calculation was performed using an estimated 120-day mortality rates of 8% and 1.7% in the control and intervention arms, respectively. These rates were extrapolated from the 90-day mortality rates of 1.7% (decompressing stoma (DS)) vs 7.2% (emergency resection (ER)) as well as the 3-year overall survival data in the propensity-score matched study by Veld, Tanis et al. [To achieve the 80% power with a (two-sided) 5% significance level using a normal curve via arcsine transformation (Cohen, 1988, Chapter 6), at least 210 patients per arm (total 420 patients) need to be analyzed. To account for an expected 10% dropout rate, the target enrollment is 468 patients (234 per arm). Considering a 20% screen-failure rate, 588 patients will need to be assessed for eligibility. The power calculations were performed using SAS Version 9.4.