Optimal design for some acelerated life tests plans / Amira Mohamed Hamdy Fathy ; Supervised Amal Soliman Hassan , Salwa Mahmoud Samy Assar ,

Thesis (Ph.D.) - Cairo University - Institute of Statistical Studies - Department of Mathematical Statistics

Products or materials are often tested at higher levels of stress than operational conditions to quickly obtain information on the life distribution or product performance under normal use. Such testing could save much time and money. In step stress accelerated life tests (SSALTs), the stress for survival units is generally changed to a higher stress level at a pre-determined time. Determination of the stress change times is one of the most important design problems in SSALTs. In this dissertation research, the point and interval estimators of the unknown parameters for Weibull Poisson (WP) distribution of multiple (k-level) SSALTs with type-I censoring data as well as the optimum time of changing stress levels and optimum censoring time using A optimality criteria are introduced. In addition, the expected Fisher information matrix is derived to obtain the optimum test plan for k-level SSALTs of Weibull Poisson distribution under type-I progressive interval censoring data using two different optimality schemes (A optimality scheme and EP inspection scheme), also point estimators of the unknown parameters are obtained to compare the two different optimality schemes

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