A parametric model for long‐term follow‐up data from phase III breast cancer clinical trials

Abstract
We propose a parametric version of a univariate gamma frailty model. The proposed model is shown to be flexible enough to model long‐term follow‐up survival data from breast cancer clinical trials when the treatment effect diminishes as time progresses, a case for which neither the proportional hazards nor proportional odds assumptions are satisfied. The observed information matrix is computed to evaluate the variances of parameter estimates. A simple parametric test statistic to test proportional odds assumption is also constructed. The model is applied to a data set from a phase III clinical trial on breast cancer. Copyright © 2003 John Wiley & Sons, Ltd.