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Variable Sampling Interval Control Charts for Monitoring the Ratio of Two Normal Variables

Huu Du NguyenThong Ngee GohKim Phuc Tran

出版	ASTM International, 2020
URL	http://books.google.com.hk/books?id=BUF3zgEACAAJ&hl=&source=gbs_api

註釋It is well documented that the distribution of the ratio between two random normal variables is asymmetric. As a consequence, the two-sided Shewhart control chart monitoring this ratio (denoted as Shewhart-RZ chart) has an average run length-biased property. In order to overcome this drawback, we propose in this article a design for two separated one-sided control charts. Furthermore, we improve the efficiency of the Shewhart-RZ chart by combining the Shewhart chart with a variable sampling interval strategy. The chart performance is then evaluated by using an average time to signal. The numerical results show that our proposed charts outperform the two-sided Shewhart-RZ control chart in detecting process shifts.