Hotelling’s T2 control chart with double warning lines

Alireza Faraz

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)


Recent studies have shown that the T 2 control chart with variable sampling intervals (VSI) and/or variable sample sizes (VSS) detects process shifts faster than the traditional T 2 chart. This article extends these studies for processes that are monitored with VSI and VSS using double warning lines (T 2 -DWL). It is assumed that the length of time the process remains in control has exponential distribution. The properties of T 2 -DWL chart are obtained using Markov chains. The results show that the T 2 -DWL chart is quicker than VSI and/or VSS charts in detecting almost all shifts in the process mean.

Original languageEnglish
Pages (from-to)569-593
Number of pages25
JournalStatistical Papers
Issue number4
Publication statusPublished - Oct 2006


  • Double Warning Lines Scheme
  • Markov chain process
  • Multivariate T control chart
  • Multivariate quality control
  • Variable sampling plan


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