Sample Size Calculation for Count Data in Comparative Clinical Trials with Nonuniform Patient Accrual and Early Dropout

Abstract

In clinical trials with counts of recurrent event data, it is often of particular interest to test whether the experimental treatment reduces the event rate in comparison with a control. The sample size calculation for such a trial often assumes fixed follow-up time for each patient. In many trials, however, we follow all patients for a predetermined follow-up time after the end of the accrual period, in which case the follow-up time is variable. This article provides methods for sample size calculation for clinical trials with ordinary Poisson count data and variable follow-up time allowing for nonuniform accrual and early dropouts. We also generalize the sample size formula to count data with overdispersion.