Quantitative techniques to evaluate process stability

Brenda S. Ramirez, George Runger

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


There have been numerous measures proposed to quantify the capability of a process using statistics such as Cp, C pk, and Cpm. There are even tests of hypothesis to see if the calculated Cp or Cpk exceeds some constant. However, there are few quantitative summaries to use as a starting point to assess the overall in-control performance of a process. In this article, we propose three measures that can be used to assess the stability of a process and classify the process parameter as stable or unstable. Test criteria for each of the three measures are suggested, and their overall performance under certain conditions are studied. These concepts are demonstrated using three case studies that are detailed throughout the article.

Original languageEnglish (US)
Pages (from-to)53-68
Number of pages16
JournalQuality Engineering
Issue number1
StatePublished - Jun 2006


  • Stability ratio
  • Statistical process control
  • Western Electric rules

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Industrial and Manufacturing Engineering


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