Cluster randomized trials (CRTs) involve the random assignment of intact social units rather than independent subjects to intervention groups. Time-to-event outcomes often are endpoints in CRTs where the intracluster correlation coefficient (ICC) serves as a descriptive parameter to assess the similarity among outcomes in a cluster. However, estimating the ICC in CRTs with time-to-event outcomes is a challenge due to the presence of censored observations. The ICC is estimated for two CRTs using the censoring indicators and observed outcomes.
A simulation study explores the effect of administrative censoring on estimating the ICC. Results show that the ICC estimators derived from censoring indicators and observed outcomes are negatively biased for positively correlated outcomes. Analytic work further supports these results. Censoring indicators may be preferred to estimate the ICC under moderate frequency of administrative censoring while the observed outcomes may be preferred under minimal frequency of administrative censoring
