On the estimation of intracluster correlation for time-to-event outcomes in cluster randomized trials.
In clinical trials, information about certain time points may be of interest in making decisions about treatment effectiveness. Therefore, rather than comparing entire survival curves, researchers may wish to focus the comparison on fixed time points with potential clinical utility. For two independent samples of right-censored data, Klein et al. (2007) compared survival probabilities at a fixed timepoint by studying a number of tests based on transformations of the Kaplan–Meier estimators of the survival function. To compare the survival probabilities at a fixed time point for paired right-censored data or clustered rightcensored data, however, their approach requires modification. In this paper, we extend the statistics to accommodate possible within-pair and within-cluster correlation. We use simulation studies to present comparative results. Finally,we illustrate the implementation of these methods using two real data sets. © 2010 Elsevier B.V. All rights reserved.