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A moving average control chart using a robust scale estimator for process dispersion
Author(s) -
Koukouvinos Christos,
Lappa Angeliki
Publication year - 2019
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.2537
Subject(s) - control chart , standard deviation , ewma chart , x bar chart , estimator , chart , control limits , statistics , statistic , mathematics , statistical process control , moving average , dispersion (optics) , normality , scale (ratio) , scale parameter , \bar x and r chart , process (computing) , computer science , physics , quantum mechanics , optics , operating system
Control charts are one of the most powerful tools used to detect and control industrial process deviations in statistical process control. In this paper, a moving average control chart based on a robust scale estimator of standard deviation, namely, the sample median absolute deviation ( M A D ) statistic, for monitoring process dispersion, is proposed. A simulation study is conducted to evaluate the performance of the proposed moving average median absolute deviation (MA‐MAD) chart, in terms of average run length for various distributions. The results show that the moving average MAD chart performs well in detecting small and moderate shifts in process dispersion, especially when the normality assumption is violated. In addition, this chart is very efficient, especially when the quality characteristic follows a skewed distribution. Numerical and simulated examples are given at the end of the paper.