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. Author manuscript; available in PMC: 2015 Jul 30.
Published in final edited form as: Stat Med. 2014 Mar 27;33(17):2897–2913. doi: 10.1002/sim.6154

Figure 4.

Figure 4

Behavior of the power and Type I error rate as a function of the correlation with sample size recalculation in four-stage group-sequential designs, where the 1st, 2nd and 3rd interim point were selected as the timing of the sample size recalculation. The planned MSS per intervention group is calculated to detect the joint difference for two endpoints with the overall power of 80% at the one-sided significance level of 2.5%, where three interims and one final analysis are to be performed. The critical values are determined by the OF boundary for both endpoints, with the LD alpha-spending method. The upper limit of recalculation sample size is n2′=λn2 with λ = 1.5. The number of replications for simulation is set to 1,000,000 for evaluation of the Type I error rate and 100,000 replications for the power (DF-1)