Effect of measurement error and autocorrelation on the X¯ chart

Abstract

Measurement error and autocorrelation often exist in quality control applications. Both have an adverse effect on the X¯ chart's performance. To counteract the undesired effect of autocorrelation, we build-up the samples with non-neighbouring items, according to the time they were produced. To counteract the undesired effect of measurement error, we measure the quality characteristic of each item of the sample several times. The chart's performance is assessed when multiple measurements are applied and the samples are built by taking one item from the production line and skipping one, two or more before selecting the next.

Keywords:

• X¯ chart
• measurement error
• first-order autoregressive model
• multiple measurements
• skipping items strategy

Acknowledgements

We would like to thank the referees. They carefully read the earlier draft and made many constructive suggestions. The first author has been supported by CNPq - National Council for Scientific and Technological Development, Project 307744/2006-0.