Lower confidence bounds as precision measure for truncated processes

Chia-Huang Wu, W.l. Pearn, Yu Ting Tai*, Pi Chuan Lin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Process capability index Cp has been the most popular one used in the manufacturing industry to provide numerical measures on process precision. For normally distributed processes with automatic fully inspections, the inspected processes follow truncated normal distributions. In this article, we provide the formulae of moments used for the Edgeworth approximation on the precision measurement Cp for truncated normally distributed processes. Based on the developed moments, lower confidence bounds with various sample sizes and confidence levels are provided and tabulated. Consequently, practitioners can use lower confidence bounds to determine whether their manufacturing processes are capable of preset precision requirements.

Original languageEnglish
Pages (from-to)1461-1480
Number of pages20
JournalCommunications in Statistics: Simulation and Computation
Issue number2
StatePublished - 7 Feb 2017


  • Lower confidence bound
  • Moments of truncated normal
  • process capability index C


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