Optimal Designs of EWMA Charts for Monitoring the Coefficient of Variation Based on Median Run Length and Expected Median Run Length

Teoh, Wei Lin and Lim, J.Y. and Khoo, Michael Boon Chong and Chong, Zhi Lin and Yeong, Wai Chung (2018) Optimal Designs of EWMA Charts for Monitoring the Coefficient of Variation Based on Median Run Length and Expected Median Run Length. Journal of Testing and Evaluation, 47 (1). p. 20170118. ISSN 0090-3973

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Official URL: https://doi.org/10.1520/JTE20170118

Abstract

The shape of run-length distribution changes with process shifts. This leads to complexity in interpreting the average run length performance. In this article, we show that the percentiles of the run-length distribution, especially the median run length (MRL), are more intuitive. The 5th and 95th percentiles of the run-length distribution are also provided in order to investigate the variation and spread of the run length. We develop two new optimal-design procedures for the exponentially weighted moving average (EWMA) charts, for monitoring the coefficient-of-variation (CV) squared (EWMA-γ2). These include minimization of the out-of-control MRL and the out-of-control expected MRL for deterministic and unknown shift sizes, respectively. Both the zero and steady states are discussed in this article. The optimal EWMA-γ2 chart is illustrated with real industrial data obtained from a metal sintering process. A comparative study reveals the superiority of the EWMA-γ2 charts for certain ranges of shifts in the CV. Copyright © 2018 by ASTM International

Item Type: Article
Uncontrolled Keywords: Coefficient of variation; Deterministic; Expected median run length; Exponentially weighted moving average chart; Median run length; Steady states; Unknown shift sizes; Zero
Subjects: H Social Sciences > HA Statistics
Divisions: Faculty of Business and Accountancy > Dept of Operations and Management Information Systems
Depositing User: Ms. Juhaida Abd Rahim
Date Deposited: 18 Dec 2019 02:50
Last Modified: 18 Dec 2019 02:50
URI: http://eprints.um.edu.my/id/eprint/23256

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