Table 2.

Sample sizes, number of events, and empirical powers in a group-sequential trials with two co-primary outcomes (Clayton copula).

Corr ρj	*FSS	Group-sequential design					Empirical power (%)
		MSS	MEN		AEN		Both EP	At least one EP	Single EP
			OC1	OC2	OC1	OC2			OC1	OC2
0.0	830	835	168	335	141	293	80.6	99.3	95.3	84.6
0.1	829	833	167	334	140	292	80.5	99.2	95.2	84.5
0.2	827	832	167	333	140	291	80.4	99.2	95.2	84.4
0.3	826	831	167	333	140	291	80.7	99.1	95.3	84.5
0.4	824	829	166	332	139	291	80.5	99.0	95.2	84.3
0.5	822	827	166	331	139	290	80.6	99.0	95.1	84.3
0.6	820	825	166	331	139	290	80.6	99.0	95.1	84.2
0.7	816	821	165	329	138	288	80.5	98.5	95.0	83.9
0.8	811	816	164	327	137	287	80.5	98.2	95.0	83.7
0.9	801	806	162	323	136	284	80.3	97.5	94.6	83.2
0.95	792	797	160	319	134	280	80.4	96.8	94.4	82.8

^*FSS:Sample sizes required for fixed-sample design.

The trial is designed to evaluate if an intervention is superior to the control with respect to both virologic (OC1) and regimen failure (OC2) with 80% power at the 2.5% significance level of a one-sided logrank test, where two analyses are planned at fixed calendar times of 48 and 96 weeks. For both outcomes, the critical boundaries are determined using the Lan-DeMets error-spending method with the O’Brien-Fleming type function. The bivariate exponential distribution is modeled using the Clayton copula. Empirical power is calculated using 100,000 repetitions. The marginal powers for OC1 and OC2 are calculated under a calculated maximum sample size.