Optimum simple step-stress plan for log-logistic cumulative exposure model

摘要

In this paper we assume that the life time of a test unit follows a log-logistic distribution. Optimum times of changing stress level for simple step-stress plans under a cumulative exposure model are obtained for a wide range of values of the model parameters. Tables of optimum times are obtained by minimizing, with respect to the change time, the asymptotic variance of the maximum likelihood estimator of a given 100 P-th percentile of the distribution at the design stress. The confidence intervals of the model parameters that based on the asymptotic normality of the maximum likelihood estimator are also obtained and i llustrated by an example.