On Small Shifts in Quality Control

Douglas M. Hawkins, K. D. Zamba

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


The Shewhart Xbar chart is effective in detecting large shifts in a process but unable to find moderate shifts. We show that this blind spot allows shifts smaller than one standard deviation to continue undetected for long periods, thereby incurring much larger total costs than do rapidly detected large shifts. Augmenting the Shewhart chart with a cumulative sum chart largely plugs this gap, leading to much more effective process monitoring.

Original languageEnglish (US)
Pages (from-to)143-149
Number of pages7
JournalQuality Engineering
Issue number1
StatePublished - Sep 2003

Bibliographical note

Funding Information:
The authors are grateful for the editor’s suggested improvements. This work was supported by the National Science Foundation under grant DMS 9803622.


  • EWMA
  • Loss function
  • Run length
  • Shewhart control chart


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