The expected average run length of the ewma median chart with estimated process parameters

You Huay Woon, Michael Khoo Boon Chong, Chong Zhi Lin, Teoh Wei Lin

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Abstract

The performance of a control chart is commonly investigated based on the assumption of known process parameters. Nevertheless, in most manufacturing and service appli-cations, the process parameters are usually unknown to practitioners. Hence, they are estimated from an in-control Phase-I samples. As such, the performance of the control chart with estimated process parameters will behave differently from the corresponding chart with known process parameters. To study this issue, the exponentially weighted moving average (EWMA) median chart is examined in this article. The EWMA median chart is traditionally investigated based on the average run length (ARL). The limitation of the ARL is that it requires practitioners to specify the shift size in advance. This phenomenon is not ideal for practitioners who do not have background knowledge of the process. In view of this, the EWMA median chart with known and estimated process parameters is studied based on the ARL and expected average run length (EARL). The results indicate that as long as the particular shift size is within the range of shifts, the performance of the chart is almost the same, for the EWMA median chart with known and estimated process parameters.

Original languageEnglish
Pages (from-to)19-24
Number of pages6
JournalAustrian Journal of Statistics
Volume49
Issue number3
Early online date20 Feb 2020
DOIs
Publication statusPublished - 3 Apr 2020

Keywords

  • Estimated process parameters
  • EWMA median chart
  • Expected average run length

ASJC Scopus subject areas

  • Statistics and Probability
  • Statistics, Probability and Uncertainty
  • Applied Mathematics

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