Effects of non-normality on economic and economic statistical designs of -control charts with multiple assignable causes and Weibull in-control times

ABSTRACT

The common assumption for designing a control chart is that the quality measurements are normally distributed, although this may not be tenable in some industrial systems. This study investigates the effects of non-normal quality data on economic and economic statistical designs of -control charts with multiple assignable causes and Weibull process failure mechanism. Numerical examples assess the performance of the multiplicity-cause model in three cases of Normal, Burr, and Johnson distributions along with the single-cause model under the same quantities of time and cost. The results reveal that the choice of quality characteristic distribution significantly affects optimal design parameters.

KEYWORDS:

• Multiple assignable causes
• Non-normal distributed data
• Increasing failure rate
• Integrated hazard over sampling interval
• Expected cost per unit time

MATHEMATICS SUBJECT CLASSIFICATION:

• 62P30

Acknowledgments

This research was carried out by Quality Research Team and supported financially by Vice-President for Research of Allameh Tabataba’i University. The authors also acknowledge the insightful comments made by the reviewers of the original version of this article.