Using the bootstrap for estimation in group sequential designs: an application to a clinical trial for nasopharyngeal...

We investigate a resampling method for bias correction in group sequential designs with censored survival data using logrank testing. The method draws nested bootstrap samples of different sizes from the observed data in order to mimic the large sample independent increment property of statistics resulting from sequential designs. The motivation for this problem came from the very positive results and early termination of a randomized clinical trial for nasopharyngeal cancer co-ordinated by the Southwest Oncology Group.