Sample Size Adjustment in Clinical Trials for Proving Equivalence

To overcome the problem of uncertainty in the planning phase of clinical trials, study designs have been proposed that allow for mid-course reestimation of the sample size. Using a study in asthma patients, we illustrate how blind sample size adjustment can be performed in an equivalence trial. Thereby, we demonstrate how the type I error rate can be controlled. Further, we show that the well-known expectation-maximization algorithm-based procedure by Gould and Shih is inappropriate for the purpose of sample size reestimation.