Auxiliary information based maximum EWMA and DEWMA charts with variable sampling intervals for process mean and variance

Abstract

The maximum EWMA (ME) and maximum double EWMA (MDE) charts are used to detect joints shifts in mean and variance of a normal process. In this paper, we propose the ME and MDE charts using the variable sampling interval (VSI) feature. In addition, the VSI feature is also attached with auxiliary information based (AIB) ME and MDE charts. Using Monte Carlo simulations, the run length characteristics of these control charts are computed. Based on detailed run length comparisons, it is found that the ME and MDE (AIB-ME and AIB-MDE) charts with VSI are more sensitive than those with fixed sampling interval. A real dataset is considered to demonstrate the implementation of proposed charts.

Keywords:

• Auxiliary information
• average run length
• average time to signal
• DEWMA and EWMA charts
• fixed and variable sampling intervals
• Monte Carlo simulation
• process mean and variance
• statistical process control

Acknowledgments

The authors are thankful to the associate editor and two anonymous reviewers for providing useful comments that led to an improved version of the article.