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On monitoring process variance with individual observations
Author(s) -
Yeh Arthur B.,
Huwang Longcheen,
McGrath Richard N.,
Zhang Zhe
Publication year - 2010
Publication title -
quality and reliability engineering international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 62
eISSN - 1099-1638
pISSN - 0748-8017
DOI - 10.1002/qre.1092
Subject(s) - x bar chart , chart , control chart , ewma chart , statistics , variance (accounting) , \bar x and r chart , mathematics , control limits , mean squared error , process (computing) , computer science , accounting , business , operating system
Abstract This paper proposes a new control chart to effectively monitor the decrease in variance of a normal process when only individual observations are available. The idea of the new control chart, which is called the exponentially weighted mean squared inverse error (EWMSI) chart, stems from the exponentially weighted mean squared error (EWMS) chart of MacGregor and Harris ( J. Qual. Technol. 1993; 25(2):106–118). Simulation studies and an example demonstrate that the lower‐sided EWMSI chart is superior to the lower‐sided EWMS chart and the lower‐sided modified EWMS (M‐EWMS) chart of Huwang et al. ( Nav. Res. Logist. 2009; 56(7):659–668) in detecting a decrease in process variance. Furthermore, the combination of a lower‐sided EWMSI chart and an upper‐sided EWMS chart is shown to outperform the two‐sided EWMS chart and the two‐sided M‐EWMS chart in monitoring the overall changes in process variance. Copyright © 2010 John Wiley & Sons, Ltd.