The performance of process capability index C s on skewed distributions

W.l. Pearn*, C. S. Chang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Wright (1995) considered a new process capability index C s , which extends the most useful index to date for processes with two-sided specification limits. C pmk proposed by Pearn, Kotz and Johnson (1992). The new index C s not only takes into account the process variation as well as the location of the process mean relative to the specification limits, but also considers the asymmetry of the distribution by incorporating a penalty for skewness. Wright (1995) investigated an estimator of C s and studied its bias and variance by simulation. The simulation study however, was restricted to normal distributions where skewness is not present. In this paper, we extend Wright's simulation study to cover some skewed distributions including chi-square, lognormal, and Weibull distributions for some parameter values. The results show that the percentage bias of the estimator increases as the skewness coefficient |μ 33

Original languageEnglish
Pages (from-to)1361-1377
Number of pages17
JournalCommunications in Statistics Part B: Simulation and Computation
Issue number4
StatePublished - 1 Jan 1997


  • Process capability indices
  • Process standard deviation, skewed distributions
  • Specification limits; process mean

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