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Exact Properties of Demerit Control Charts

Summary: [This abstract is based on the authors' abstract.] A demerit rating system is used to simultaneously monitor counts of several types of defects in a complex product. The demerit statistic is a linear combination of the counts of these types of defects. The traditional recommendation is to plot the demerit statistic on a control chart with symmetric 3-sigma control limits. This approach is reviewed. An alternative method for determining control limits for the demerit control chart is proposed. The proposed method is based on the exact distribution of linear combinations of independent Poisson random variables. A generalization of the method covers the exact distribution of linear combinations of independent random variables in a broad family of discrete distributions.

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  • Topics: Quality Tools, Statistical Process Control (SPC)
  • Keywords: Attributes control charts,Control charts,Statistical process control (SPC)
  • Author: Jones, L. Allison; Woodall, William H.; Conerly, Michael D.
  • Journal: Journal of Quality Technology