One-sided α β1 0.1 0.2 0.3 ≥0.4
0.025 α2 0.3000 0.2250 0.2236 0.2236
0.05 α2 0.5500 0.3500 0.3167 0.3162
Source: Chang [19].Statistics in Medicine, 26, 2772-2784.
Table 4: Stopping boundaries for two-stage futility design.