Joint Monitoring of Process Mean and Variance Using Exponentially Weighted Moving Average Control Charts


Gan, F.F.   (1995, American Statistical Association and ASQC)   National University of Singapore, Republic of Singapore

Technometrics    Vol. 37    No. 4
QICID: 13622    November 1995    pp. 446-453
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Article Abstract

The performances of control-charting schemes for the joint monitoring of a process mean and a variance are evaluated and compared. Certain schemes are shown to be inadequate for this purpose, and the potential risk of using these schemes alone is discussed. A combined scheme consisting of a two-sided exponentially weighted moving average (EWMA) mean chart and a two-sided EWMA variance chart is found to perform well under several types of out-of-control situations. A simple method is provided for approximating the average run length and the percentage points of a run-length distribution of a combined EWMA scheme. A simple procedure is also proposed for the design of a combined EWMA scheme.


Average run length (ARL),Statistical methods,Run length,Normal distribution,Statistical quality control (SQC)

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