Monitoring the coefficient of variation using a variable sample size and sampling interval control chart

ABSTRACT

This article proposes a CV chart by using the variable sample size and sampling interval (VSSI) feature to improve the performance of the basic CV chart, for detecting small and moderate shifts in the CV. The proposed VSSI CV chart is designed by allowing the sample size and the sampling interval to vary. The VSSI CV chart's statistical performance is measured by using the average time to signal (ATS) and expected average time to signal (EATS) criteria and is compared with that of existing CV charts. The Markov chain approach is employed in the design of the chart.

KEYWORDS:

• Average time to signal
• Coefficient of variation
• Expected average time to signal
• Markov chain
• Variable sample size and sampling interval

MATHEMATICS SUBJECT CLASSIFICATION:

• Primary 90B25
• Secondary 62P30

Acknowledgments

This work is supported by the MyBrain15 (MyPhD) Scholarship Program under the Ministry of Higher Education Malaysia and is funded by the Universiti Sains Malaysia, Research University Grant, number 1001/PMATHS/811263.