p Prime or Laney p Chart Formulas

The p prime chart (p' chart or modified p chart) works much like an XmR chart.

  1. Convert the p values to z values.
  2. Calculate the moving range of the z values.
  3. Use these values to calculate sigma-estimator.
  4. Use the sigma estimator to adjust the control limits.

Here are the formulas used to calculate a p prime chart.

laney p chart formula

Source: Improved Control Charts for Attributes, David B. Laney © 2002

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The p prime chart is just one of the tools included in the QI Macros for Excel SPC Software for Excel.


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