Time Savings in Censored Life Testing

Summary It is often possible to achieve a saving of time in a life testing experiment by allowing right-censoring. This concept is important in clinical trials in which an early decision procedure is used. We describe the use of the ratio of order statistics as a measure of time savings, and give results on the distribution of such ratios. Numerical results are tabled and discussed for several underlying distributions of failure time (uniform, exponential, Pareto). We outline the application of this approach to the evaluation of early stopping procedures, with particular emphasis on analysing the time savings achieved by two-sample rank tests.