Table 1.

Empirical global type I error rates, empirical significance level for each endpoint and proportion of not terminating the trial early assuming equal allocation of type I error rate of 0.025 for each endpoint and using O’Brien-Fleming boundaries; results based on 10,000 simulations

Type of Copula	τ	Empirical Global Type I	PFS			OS
		Error Rate	1st Interim	Final Analysis	Type I Error	1st Interim	Final Analysis	Type I Error
Type-I error rate		0.05	0.00146	0.02441	0.025	0.00146	0.02441	0.025
Independence	0	0.051	0.0015	0.0244	0.0259	0.0015	0.0251	0.0257
Normal	0.10	0.050	0.0017	0.0226	0.0243	0.0023	0.0254	0.0265
	0.30	0.047	0.0013	0.0219	0.0232	0.0022	0.0259	0.0267
	0.50	0.047	0.0021	0.0251	0.0273	0.0017	0.0255	0.0264
	0.70	0.039	0.0005	0.0224	0.0229	0.0019	0.0259	0.0265
Frank	0.10	0.051	0.0017	0.0254	0.0271	0.0012	0.0242	0.0247
	0.30	0.044	0.0014	0.0228	0.0242	0.0012	0.0217	0.0221
	0.50	0.046	0.0016	0.0244	0.0260	0.0014	0.0247	0.0253
	0.70	0.040	0.0020	0.0234	0.0254	0.0017	0.0217	0.0226
Gumbel	0.10	0.046	0.0014	0.0210	0.0224	0.0012	0.0246	0.0248
	0.30	0.051	0.0016	0.0230	0.0246	0.0017	0.0283	0.0286
	0.50	0.041	0.0014	0.0220	0.0234	0.0016	0.0220	0.0227
	0.70	0.042	0.0015	0.0257	0.0257	0.0018	0.0246	0.0253