Monitoring the coefficient of variation using variable sampling interval CUSUM control charts

Abstract

In monitoring the coefficient of variation (CV), the variable sampling interval (VSI) type charts are a useful adaptive strategy that has been recently combined with various types of charts, including exponentially weighted moving average (EWMA) and variable sample size (VSS) charts. These combinations lead to desirable control charts with an impressive performance in detecting process shifts or anomalies. However, in these studies, the authors asserted that adaptive type charts are not competitive to monitor downward shifts in the CV. Therefore, they willingly omitted the decrease in process shifts. In this paper, we suggest overcoming this downside by designing two one-sided VSI CUSUM control charts for tracking the CV. The performance of the proposed charts is evaluated by the average time to signal (ATS) criterion. The numerical results show that our proposed adaptive type charts are efficient charts to monitor downward shifts in the CV.

Keywords:

• VSI
• CUSUM
• coefficient of variation
• Markov chain
• anomaly detection

2010 Mathematics Subject Classifications:

• 60J10
• 62P30

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Acknowledgements

The authors would like to thank the anonymous referees for their valuable suggestions that helped to improve the quality of the final manuscript. The corresponding author, Phuong Hanh Tran, would like to gratefully acknowledge the financial support from Vietnam International Education Development (VIED) - Project 911 for her research activities.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Research activities of Phuong Hanh Tran have been funded by Vietnam International Education Development [Project 911].