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# A Method to Enhance the Performance in the Construction of the Moving Average S Chart

Khoo, Michael B.C., and Looi C.Y., (2006) A Method to Enhance the Performance in the Construction of the Moving Average S Chart. Matematika, 22 (1). pp. 67-76. ISSN 01278274

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## Affiliations

Universiti Sains Malaysia, School of Mathematical Studies
Universiti Sains Malaysia, School of Mathemnatical Studies

## Abstract

The S chart is often used to monitor shifts in the process variance in industries. The S chart is different from the R chart because the S chart is based on the sample standard deviation whereas the R chart involves the sample range. The S chart is less sensitive in the detection of small shifts in the variance. In this study a method to enhance the performance of the S chart by means of the construction of the moving average S chart will be proposed. A simulation study is conducted using SAS version 8 to evaluate the performance of the moving average S chart. Average and median run lengths are computed so that a comparison of the performances between the moving average S chart and the basic S chart can be made. The average run length (ARL) and median run length (MRL) give the average and median of the number of samples that must be plotted on a control chart before the first out-of-control signal is received. These two measures evaluate the quickness of a control chart in detecting a shift in the process. The advantages of MRL as compared to ARL are also discussed in this study.

Item Type: Journal Moving average S chart, S chart, average run length (ARL), median run length (MRL), variance process, out-of-control signal, type-I-error Q Science, Computer Science 5931

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