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Comparisons of Exponential Life Test Plans with Intermittent Inspections

Summary: [This abstract is based on the author's abstract. A longer abstract is available on the journal's website.]

Most existing life test plans involve life tests conducted under continuous inspection of life items. A reduction in testing effort and administrative convenience may be obtained by using intermittent inspection whereby items are inspected only a certain points in time. The hybrid plan, which uses a single inspection at the censoring time, is often used in practice. To determine whether adding more inspections to the hybrid plan improves its statistical performance substantially, a life test plan with multiple inspections is developed assuming that the lifetimes of items follow an exponential distribution. For multiple inspection times, equally-spaced, equal-probability, and equally-spaced in log-time inspection plans are considered. The developed plan is then compared to the hybrid and Type I-censored life test plan with continuous inspection in terms of the sample size required, the expected completion time to reach a decision, and the power of test. Computational results indicate that these performance measures are relatively insensitive to the inspection plan used. This implies that the equally-spaced inspection scheme may be considered appropriate, since it is more convenient to schedule and does not require a priori information on unknown parameters. Additionally, researchers found that the life test plan with multiple inspections is the preferred choice when the discrimination ratio is small and the censoring time is large. In general, however, conducting more than one inspection does not improve statistical performances substantially, and the hybrid plan is recommended.

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  • Topics: Data Quality, Inspection
  • Keywords: Statistical design,Censored data,Inspection,Manufacturing
  • Author: Kim, Sun-Ho; Yum, Bong-Jin
  • Journal: Journal of Quality Technology