Monitoring process variability using auxiliary information |
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Authors: | Muhammad Riaz |
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Institution: | (1) Department of Statistics, Quaid-i-Azam University, Islamabad, Pakistan |
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Abstract: | In this study a Shewhart type control chart namely V
r
chart is proposed for improved monitoring of process variability (targeting large shifts) of a quality characteristic of
interest Y. The proposed control chart is based on regression type estimator of variance using a single auxiliary variable X. It is assumed that (Y, X) follow a bivariate normal distribution. The design structure of V
r
chart is developed and its comparison is made with the well-known Shewhart control chart namely S
2 chart used for the same purpose. Using power curves as a performance measure it is observed that V
r
chart outperforms the S
2 chart for detecting moderate to large shifts, which is main target of Shewhart type control charts, in process variability
under certain conditions on ρ
yx
. These efficiency conditions on ρ
yx
are also obtained for V
r
chart in this study. |
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Keywords: | Control charts Power curves Simulations S 2 chart V r chart Normality Auxiliary information |
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