GENERALIZED VARIANCE CHART DESIGN WITH ADAPTIVE SAMPLE SIZES. THE BIVARIATE CASE

Abstract

Multivariate Statistical Quality Control has recently become a basic tool in process control. Various control charting procedures have been proposed when several quality characteristics are to be monitored simultaneously, for example, the mean and covariance matrix of a multivariate quality measurement. On the other hand, it has been showed that many of the charts usually employed are not powerful enough to detect small changes in the process. The use of adaptive sample size is one of the methods that offers the best results to increase the power. The present work shows the design of the Generalized Variance Chart |S| with adaptive sample size to control processes defined by two quality characteristics, comparing the power of this new chart versus the |S| chart with fixed sample size.

Keywords:

• SPC
• Multivariate statistical quality control
• Generalized variance chart
• Determinant ratio

ACKNOWLEDGMENT

The authors wish to thank the referees for their thoughtful suggestions that improved the final version of this paper.