Type of Copula      τ 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

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.