ACCURACY OF APPROX CONFIDENCE-BOUNDS USING CENSORED WEIBULL REGRESSION DATA FROM ACCELERATED LIFE TESTS

For censored Weibull regression data arising from typical accelerated life tests (ALTs), the performance of small-sample normal-theory confidence intervals is summarized by three points: (1) they have highly asymmetric error rates; (2) they can be extremely anti-conservative; and (3) these effects worsen when higher confidence levels are used. Likelihood-ratio-based confidence intervals have much more symmetric error rates which are not as extremely anti-conservative as normal-theory intervals can be. For typical ALTs, likelihood-ratio-based confidence intervals are better than those based on asymptotic normal theory. Likelihood-ratio-based confidence intervals require more computation than intervals based on the asymptotic normality of the maximum-likelihood estimators. The resource spent on computing is, however, usually very small compared to the other costs involved in an ALT.