Sample size {14}
cirrhosis
REGRESSION, CIRRHOSIS, RECRUITMENT, COMPLICATIONS
The sample size estimation is based on the primary outcome transplant-free survival (LTX-OS) and two-sided log-rank test. Previous data suggest that type 1 HRS who received TIPS had a 64% survival at 3 months, with a 20% 1-year survival [Because of the change in the definition of HRS, the patients in the present study will be in a slightly better shape, so an estimated 3-month survival rate of 50% (exponential parameter 0.231) in the control and 70% (exponential parameter 0.1189) in the experimental group (resulting in a hazard ratio HR = 0.51) are expected. With a significance level of 5%, power of 90%, recruitment period of 24 months, individual follow-up of 12 months, and dropout rate of 10% (exponential parameter 0.0088), 56 patients are needed in each group.Due to the expected additional T-to-C-switcher (patients, randomized in the TIPS-group, but who are not in the constitution for this procedure) between randomization and TIPS procedure, 62 patients will be randomized to each group (124 patients overall). Although there are no data regarding this, from clinical experience we believe that this will happen in approximately 10% of patients. As the adjusted Cox regression analysis is more powerful than the log-rank test, this sample size calculation is considered to be conservative. Furthermore, patients who are initially assigned to the C group may develop during follow-up complications of cirrhosis in which TIPS placement is indicated. There is no clear-cut data about the number of patients in whom this will occur and hence drop in TIPS treatment (C-to-T-switcher). Assuming that this number will be low, a relatively high power of 90% was chosen to account for possible switchers, and the sample size is calculated without this information.