One-sided α α1 0.005 0.010 0.015 0.020 0.025 0.030 0.025 α2 0.2050 0.1832 0.1564 0.1200 0.0250 - 0.05 α3 0.3050 0.2928 0.2796 0.2649 0.2486 0.2300

Source: Chang [19] Statistics in Medicine, 26, 2772-2784.

Table 2: Stopping boundaries for two-stage efficacy designs.