Concordance correlation in the measurements of time to event.

The concordance correlation coefficient (CCC), a measure of concordance in ratings from multiple raters, was used to study inter-rater agreement in measurements of time to event, generally not observed with perfect consistency among raters. As a function of the first two moments of rating measures, the CCC can be estimated with data subject to censoring, using a likelihood-based estimation method applied under the assumptions of random censoring and parametric distribution models for the ratings of time to event. A simulation study was conducted for small sample performance under various censoring proportions. The use of the CCC with censored data is illustrated with an example taken from a data set containing data on time to an event with two raters per subject. Copyright 2004 John Wiley & Sons, Ltd.