Failure-Censored Variables-Sampling Plans for Lognormal and Weibull Distributions

Variables-sampling plans arc more efficient than attributes-sampling plans. If the quality characteristic is the life of a product. however, variables sampling can be very time consuming and expensive. To save time and money, tests can be terminated before all test units have failed. This article discusses the design of variables-sampling plans based on failure-censored samples. This method of design can be applied to lognormal-distributed and Wcibull-distributed lifetimes. An example for lognormal-distributed lifetimes will be given. Although the method is based on asymptotic results, Monte Carlo simulations for lognormal and Weibull lifetimes show that the sampling plans meet the required risks when bias corrected maximum likelihood estimators for the location and scale parameters are used. The advantage of failurecensored sampling plans is that they require a much smaller sample size than attributes-sampling plans and a greatly reduced test time when compared to complete variables-sampling plans.