Life Test Sampling Plans for Normal and Lognormal Distributions

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Abstract
Sampling plans for truncated life tests from the normal and lognormal distributions are obtained. The tables of this paper give the minimum sample size necessary to assure a certain mean or median life when the experiment time is tied in advance. The modification necessary to assure any other quantile (percentile) of the distributions is obtained. Thus, sampling plans for establishing other percentiles of the distributions are shown to be obtainable from the tables of this paper. The operating characteristic functions of these plans are obtained and for a wide range of values of practical interest these functions are graphed in order to facilitate selection of an appropriate plan in a given situation. Producer's risk is discussed and a table is given for the ratio of the true median life to the specified median life (or the difference between the true mean lie and the specified mean life) to insure that the producer's risk does not exceed α = .l0, .05. An approximation is given for the minimum sample size. The use of tables and graphs is illustrated by examples.

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