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by Dr. Feng-Bin (Frank) Sun
Classical reliability engineering and life data analysis typically deal with two distinctive data categories: failure time and survival time. The status of each unit under test (UUT) is classified as either “failure” or “survival”. That is, the counts of failures and counts of survivors are always an integer number. In the meantime, most of the statistical and reliability-related software packages were designed to accept only the integer counts for both failures and survivors. The corresponding data entry format and underlying data analysis algorithm, such as parameter estimation using maximum likelihood estimation (MLE) method, were structured to accommodate integer failure and survivor only. However, in real world practice, fractional failures (and therefore fractional survivors as well) can be encountered at various scenarios.