Multi-attribute unit and group runs control chart to identify the process deterioration

Abstract

Gadre and Rattihalli [Gadre, M.P. and Rattihalli, R.N., 2005a, A unit and group runs based chart to identify increases in fraction nonconforming. Journal of Quality Technology, 37, 199–209.] proposed a control chart called the unit and group runs (UGR) control chart to identify increases in fraction non-conforming. In this article, the concept of UGR chart is extended to the multi-attribute case to detect the process deterioration. It is illustrated that in multi-attribute cases also, the UGR chart gives a remarkable reduction in out-of-control average time to signal when compared with the multi-attribute np chart, the multi-attribute synthetic chart and the multi-attribute group runs chart recently developed by Gadre and Rattihalli [Gadre, M.P. and Rattihalli, R.N., 2005b, Some group inspection based multi-attribute control charts. Economic Quality Control, 20, 191–204.]. The steady state performance of the multi-attribute UGR chart is also excellent. The procedure of identifying the attributes causing signal is also described and illustrated.

Keywords:

• Average time to signal
• Bernoulli CUSUM chart
• Multi-attribute control chart
• Run-length CUSUM chart
• Steady state
• Synthetic control chart

Acknowledgements

The first author is thankful to Mr. Kalyan Joshi (SAS, Pune, India) for his help in writing the macro in Mat-Lab. We are also thankful to the referee and the associate editor for their valuable comments and suggestions that helped in improving the manuscript significantly.