Monitoring the coefficient of variation using a variable sampling interval ewma chart

W. C. Yeong, Michael B.C. Khoo, L. K. Tham, W. L. Teoh, M. A. Rahim

Research output: Contribution to journalArticlepeer-review

49 Citations (Scopus)


In recent years, the coefficient of variation (CV) chart is receiving increasing attention in quality control. A number of studies demonstrated that adaptive charts could detect process shifts faster than traditional charts. This paper proposes an EWMA chart with variable sampling interval (VSI) to monitor the CV. Formulas for computing the performance measures of the VSI EWMA-γ2; chart are derived using Markov chain, where γ2 denotes the CV squared. Comparative studies show that the VSI EWMA-γ2 chart significantly outperforms other competing charts. An example using real manufacturing data shows that the VSI EWMA-γ2 chart performs well in applications.

Original languageEnglish
Pages (from-to)380-401
Number of pages22
JournalJournal of Quality Technology
Issue number4
Publication statusPublished - 21 Nov 2017


  • Average Time to Signal
  • Expected Average Time to Signal
  • Exponentially Weighted Moving Average Chart
  • Markov Chain

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Strategy and Management
  • Management Science and Operations Research
  • Industrial and Manufacturing Engineering


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