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Trimmed Mean X-Bar and R Charts

Summary: A modified approach to the computation of control limits for X-bar and R charts is introduced. This procedure consists of replacing X-double bar with the trimmed mean of a subgroup averages, and R-bar with the trimmed mean of the subgroup ranges. Standard tables of control limits may continue to be used, requiring only adjustment by a constant multiplier, which is tabulated. The proposed control chart limits are shown to be less influenced by extreme observations than their classical counterparts, and to lead to tighter limits in the presence of out-of-control observations. These concepts are illustrated by several examples.

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  • Topics: Statistics
  • Keywords: Control charts,Statistics
  • Author: Iglewicz, Boris; Langenberg, Patricia
  • Journal: Journal of Quality Technology