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Table 1 Performance characteristics for the group sequential design with “optimal” futility boundaries based on different admissible condition parameters for N=182 and N=140. The last lines in the two sample size settings show the performance characteristics for the arbitrary choice of α0=0.5

From: Optimality criteria for futility stopping boundaries for group sequential designs with a continuous endpoint

Sample Admissible condition “Optimal” futility Actual Probability of wrongly Probability of correctly
size parameters boundary power stopping for futility stopping for futility
n Powloss πwrong α0,opt under Δ=0.5 \(P_{\Delta _{\text {true}}=0.5}\left (p_{1}>\alpha _{0}\right)\) \(P_{\Delta _{\text {true}}=0.25}\left (p_{1}>\alpha _{0}\right)\) \(P_{\Delta _{\text {true}}=0.0}\left (p_{1}>\alpha _{0}\right)\)
188 0.01 0.01 0.46 0.90 0.01 0.13 0.54
  0.05 0.01 0.46 0.90 0.01 0.13 0.54
  0.01 0.05 0.29 0.89 0.03 0.26 0.71
  0.05 0.05 0.22 0.89 0.05 0.33 0.78
  0.01 0.10 0.29 0.89 0.03 0.26 0.71
  0.05 0.10 0.13 0.85 0.10 0.47 0.87
  0.0013 0.008 0.50 0.90 0.01 0.11 0.50
140 0.01 0.01 0.59 0.80 0.01 0.10 0.41
  0.05 0.01 0.59 0.80 0.01 0.10 0.41
  0.01 0.05 0.33 0.79 0.05 0.27 0.67
  0.05 0.05 0.33 0.79 0.05 0.27 0.67
  0.01 0.10 0.32 0.79 0.05 0.28 0.68
  0.05 0.10 0.21 0.77 0.10 0.41 0.79
  0.0013 0.018 0.50 0.80 0.02 0.15 0.50