50 75 100 125 −4 −2 0 2 4 6 E(N  | 1  =  2  =  3  =  ) Design Delta = −0.25 Delta = 0 Delta = 0.25 Delta = 0.50 L = 1 200 300 400 −4 −2 0 2 4 6 E(O  | 1  =  2  =  3  =  ) Design Delta = −0.25 Delta = 0 Delta = 0.25 Delta = 0.50 L = 1 Figure 3: Performance Measurement Curves. Expected sample size and expected number of observations curves of the single-stage ( L = 1) and considered group sequential designs across a range of values of the true response rate in the experimental treatment arms θ . 15