This article examines the performance of two families of non-Normal process capability indices, using a comprehensive simulation study with data generated from the Johnson family of distributions. This study shows that none of the three indices can be classified as good estimators when the process fallout or tail probabilities are used as the indicator for measuring product quality. As a result, the two families do not demonstrate a systematic pattern to deal with non-Normal process data. Clearly, the use of the sample range is not sufficiently precise to provide an appropriate denominator for these indices. More sophisticated estimators should be considered to improve the performance of these non-Normal capability indices.
All Science Journal Classification (ASJC) codes
- Safety, Risk, Reliability and Quality
- Industrial and Manufacturing Engineering