On Improved Monitoring of Process Variability

by Muhammad Riaz .

Abstract: In this study a Shewhart type control chart namely chart is proposed for improved monitoring of process variability (targeting moderate and large shifts which is major concern of Shewhart type control charts) of a quality characteristic of interest Y. The proposed control chart is an improvement over conventionalchart to monitor process variance using a single auxiliary variable X. Assuming bivariate normality of (Y, X), design structure of chart is developed and its comparison is made with the well-known Shewhart control chart namely chart. Using power curves as a performance measure it is observed that chart outperforms the chart under certain conditions on, where is correlation (linear relationship) between Y and X. It is observed that the performance of chart keeps improving with an increase in. The efficiency conditions on are also obtained for chart where it outshines the conventional chart.

Key Words: Auxiliary Information; Control charts; Normality; Power curves; chart; chart.

Author:
Muhammad Riaz, riaz76qau@yahoo.com

Editor: Ravi Khattree, khattree@oakland.edu

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