Recurrent events data such as epileptic seizures and recurrence of superficial bladder cancer are frequently encountered in medical researches when individuals may experience multiple events of the same type. The analysis of recurrent events is complicated because related recurrent events within a subject are correlated and we need to take into account the dependence of responses from the same subject to draw valid statistical inferences. In principle, statistical strategies are classified into two approaches. The one is we focus on the number of events occurring within defined time intervals and compare / model the event rate (number of events per unit of time). The other is the recurrence times are viewed as multivariate failure times and survival analysis methods are applied. According to this perspective, we review several statistical methods to analyze recurrent events data and illustrate the techniques with real medical applications. We recommend that the choice of the endpoint (effect measure) and the corresponding statistical analysis method should be determined by the study purpose. Robust methods for the assumption of event occurring process should be used especially for analyzing confirmatory studies.
