On t and EWMA t charts for monitoring changes in the process mean
Article first published online: 6 MAR 2009
Copyright © 2009 John Wiley & Sons, Ltd.
Quality and Reliability Engineering International
Volume 25, Issue 8, pages 933–945, December 2009
How to Cite
Zhang, L., Chen, G. and Castagliola, P. (2009), On t and EWMA t charts for monitoring changes in the process mean. Qual. Reliab. Engng. Int., 25: 933–945. doi: 10.1002/qre.1012
- Issue published online: 16 NOV 2009
- Article first published online: 6 MAR 2009
- X̄ chart;
- t chart;
The performance of an X-bar chart is usually studied under the assumption that the process standard deviation is well estimated and does not change. This is, of course, not always the case in practice. We find that X-bar charts are not robust against errors in estimating the process standard deviation or changing standard deviation. In this paper we discuss the use of a t chart and an exponentially weighted moving average (EWMA) t chart to monitor the process mean. We determine the optimal control limits for the EWMA t chart and show that this chart has the desired robustness property. Copyright © 2009 John Wiley & Sons, Ltd.