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Control Charts for Short Runs: Nonconstant Process and Measurement Error

Summary: When the usual assumption of constant variances does not hold, the recommended substitute for a deviations from nominal (DNOM) chart is to chart standardized deviations. This has the added difficulty of estimating different standard deviations for each subgroup. As an alternative to this, an approach to DNOM charts that allows more general process and measurement error models is presented. When applied to the constant variance case, the usual chart of differences from nominal results. When applied to the constant coefficient of variation case, a new DNOM chart based on ratios of subgroup means to nominals results. Both charts have the desirable feature of constant control limits.

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  • Topics:
  • Keywords: Control charts,Deviation,Short runs
  • Author: Farnum, Nicholas
  • Journal: Journal of Quality Technology