Sample Size Estimation for Trials of Recurrent Events

In some clinical trials, repeated occurrences of the same type of event are the study endpoint. For example, numbers of adverse event of interest occurred during the study period. There are several standard statistical methods for the analysis of such data, including the Anderson-Gill model (Anderson and Gill, 1982) and the Poisson regression model (Frome et. al. 1973). Signorini (1991) has proposed a method to estimate power for the Poisson model in the similar situation, but no approaches to power calculations are available for the Anderson-Gill model. We illustrate SAS macro to implement Signorini's method and extend it to incorporate unequal randomization between the treatment and control groups. Furthermore, using simulations, we show that the power for both the Poisson model and the Anderson-Gill model are similar under a variety of scenarios, so that this approach to sample size calculations can be used for either method of analysis in a study.