| Summary: | In this paper, we investigate parameter inference for four-unit hybrid systems based on Type-II progressively hybrid censored and masked data from constant-stress partially accelerated life test. It is assumed that the unit lifetime in systems has exponential hazard rate. The maximum likelihood estimations (MLEs) for unknown parameters and acceleration factor are obtained. The observed Fisher information matrix, as well as the asymptotic variance-covariance matrix of the MLEs are derived. Approximate confidence intervals (CIs) and studentized-t bootstrap CIs for the parameters are presented based on normal approximation to the asymptotic distribution of MLEs and bootstrap method, respectively. A Monte Carlo simulation study is carried out to investigate the performance of the MLEs and to compare the effects of two different CIs in terms of interval length and coverage percentage for the parameters.
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