Planning survival studies to compare a treatment to an active control

Rubinstein et al. presented a procedure for determining the required duration of accrual for a clinical trial comparing the survival distributions of two treatments using a classical hypothesis testing formulation. Here their testing procedure is modified in two ways. First, the asymptotic variances used in computation of the probabilities of type I and type II errors are based on the values of the parameters specified by the null and alternative hypotheses, respectively. Second, the null hypothesis is modified for situations where it is desired to show that the experimental treatment is better or not much worse than the control.