Laney p' Chart (p Prime) Formulas
QI Macros Can Calculate Them For You!
Create a Laney p Chart using QI Macros
- Select your data.
- Select the chart on QI Macros menu.
- QI Macros will do the math and draw the graph for you.
Go Deeper:
The Laney p' Chart (p Prime or Modified p Chart) works much like an XmR Chart.
- Convert the p values to z values.
- Calculate the moving range of the z values.
- Use these values to calculate sigma-estimator.
- Use the sigma estimator to adjust the control limits.
Here are the formulas used to calculate a Laney p' Chart (p Prime):
Source: Improved Control Charts for Attributes, David B. Laney © 2002
NOTE: It is not possible to have negative limits on a p' Chart. With that, any calculated value that is below 0 is automatically changed to 0.
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The Laney p' Chart (p Prime) is just one of the tools included in QI Macros SPC Software for Excel.
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