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Reviews of Standards and Specifications: MTBF Confidence Bounds Based on MIL-STD-781C Fixed Length Test Results

Summary: Exact confidence bounds are available for the parameter ( of an exponential distribution in the case of Type II (failure) censored samples, but not in the case of Type I (time) censored samples. In the latter case, the conventional confidence bounds are conservative; Cox has proposed approximate confidence bounds which may not be conservative, but have other advantages. For MIL-STD-781C fixed-length tests, we have a mixture of the two types of censoring, Type II for rejected lots and Type I for accepted lots. Epstein proposes combining the exact bounds for rejected lots with the conventional bound for accepted lots. We propose replacing the latter by Cox's approximate bounds, and show that this gives true confidence levels closer to the nominal levels.

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  • Topics: Standards
  • Keywords: Mean time between failures (MTBF),Fixed-effects model,Standards and specifications
  • Author: Harter, H. Leon
  • Journal: Journal of Quality Technology