Group Sequential Procedures for Poisson Process Data with Frailty

Consider studies with recurrent events data modeled by local Poisson processes with frailty, or random eeects. In a group sequential design, the increments of the test statistics are no longer independent. We explore the innuences of the frailty, and tabulate the stopping boundaries and sample size ratios to control the overall type-I and type-II error rates. Applications in an animal trial with recurrent tumors are discussed, using the procedures such as the group sequential tests and the repeated conndence intervals. Minimal cost analysis is considered for determining the optimal combination of study duration and sample size.