One-sided α       β1=0.15     0.025 α1 0.005 0.010 0.015 0.020 0.025   α2 0.2154 0.1871 0.1566 0.1200 0.0250 0.05 α3 0.005 0.010 0.015 0.020 0.025   α4 0.3333 0.3155 0.2967 0.2767 0.2554

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

Table 3: Stopping boundaries for two-stage efficacy and futility designs.