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QICID: 11922
Title: Applications of the EWMA for Algorithmic Statistical Process Control
Copyright: 1994, Marcel Dekker, Inc. and ASQC
Author: Baxley, Robert V., Jr.
Organization: Monsanto Chemical Group, Gonzalez, FL
Subject: Statistical process control (SPC),Shewhart control chart,Statistical tests,Time series,Error,Statistical methods,Problem solving,Overadjustment,Simulations;
Series: Quality Engineering, Vol. 7, No. 2, December 1994, pp. 397-418
Abstract: Use of the Exponentially Weighted Moving Average (EWMA) statistic is considered for implementation of a statistical control strategy for drifting processes. This strategy keeps the process centered at the target by making process adjustments; at the same time, it detects sudden large shifts for which troubleshooting is necessary. In the past, Monsanto has typically used a modified Shewhart chart with runs rules to determine process adjustments. This new EWMA strategy is shown to be an improvement because of better tuning capability, robustness to incorrect tuning, and a decreased tendency to cause additional variability with large, inappropriate adjustments. These improvements are illustrated in two case studies involving important nylon carpet fiber quality parameters.
Number of pages: 22
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