One-sided capability indices CPU and CPL: Decision making with sample information

W.l. Pearn, K. S. Chen

Research output: Contribution to journalArticlepeer-review

71 Scopus citations


Process capability indices have been used in the manufacturing industry to provide quantitative measures on process potential and performance. The formulae for these indices are easy to understand and straightforward to apply. But, since sample data must be collected in order to calculate these indices, a great degree of uncertainty may be introduced into capability assessments due to sampling errors. Currently, most practitioners simply look at the value of the index calculated from the sample data and then make a conclusion on whether their processes meet the capability requirement. This approach is not reliable since sampling errors are ignored. Procedures for two-sided capability indices, Cp, Cpk, and Cpm have been developed to assist practitioners to determine whether their processes meet the capability requirement based on sample information. In this paper, we first obtain unbiased estimators of CPU and CPL. We then develop a procedure similar to those of Cp, Cpk, and Cpm, for the one-sided capability indices CPU and CPL. Practitioners can use the procedure to test whether their processes meet the capability requirement.

Original languageEnglish
Pages (from-to)221-245
Number of pages25
JournalInternational Journal of Quality & Reliability Management
Issue number3
StatePublished - 1 May 2002


  • Modelling
  • Process control
  • Quantitative techniques
  • Sampling techniques

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