Procedures with Equally Sized Stages
In this chapter, we describe group sequential test procedures that are designed for equal sample sizes per stage of the group sequential trial. The procedures that were originally developed in the literature (which we refer to as classical group sequential designs) make this assumption. In practice, the situation with equally sized stages often occurs. Namely, in all cases when there is no specific reason for assuming different stage sizes the sample sizes per stage should be the same.We introduce the designs due to O’Brien and Fleming (Biometrics 35:549–556, 1979), Pocock (Biometrika 64:191–199, 1977) and the power family of Wang and Tsiatis (Biometrics 43:193–199) and describe their basic properties. We also introduce the Pampallona and Tsiatis (Journal of Statistical Planning and Inference 42:19–35, 1994)symmetric design. The one-sided testing in group sequential designs is then described, together with a discussion of the stopping for futility issue in sequential designs. A note on two-sided tests in group sequential designs finalizes the chapter.
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