Monitoring the ratio of two normal variables using variable sampling interval exponentially weighted moving average control charts
(2018) , 29 pages
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ISBADP2018_34_heuchenne_MonitoringtheRatiooftwoNormalVariablesusingVariableSamplingIntervalEWMAcontrolcharts_dial.pdf
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- Abstract
- We investigate in this paper new control charts called VSI EWMA- RZ by integrating the variable sampling interval feature (VSI) with the exponentially weighted moving average (EWMA) scheme to monitor the ratio of two normal random variables. Because the distribution of the ratio is skewed, we suggest to design two separated one-sided charts instead of one two-sided chart. A new coefficient are introduced allowing us to be free to choose the value of sampling interval optimizing the performance of the control chart. We also make a direct comparison between the VSI EWMA-RZ charts and standard EWMA control chart. The numerical results show that our proposed charts outperform the standard EWMA charts in detecting process shifts. An application is illustrated for the implementation of the VSI EWMA control charts in the food industry.
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Citations
Nguyen, H. D., Tran, K. P., & Heuchenne, C. (2018). Monitoring the ratio of two normal variables using variable sampling interval exponentially weighted moving average control charts (ISBA Discussion Paper 2018/34). https://hdl.handle.net/2078.5/173731