Struggling to create a Laney p' Chart | p Prime Control Chart?
QI Macros can draw one for you in seconds, right in Excel.
Draw a p' Chart using QI Macros
- Select your data.
- Click on QI Macros menu > Control Charts (SPC) > Attribute> p' Laney.
- QI Macros will do the math and draw the graph for you.
When should you use a laney p' chart?
p Charts evaluate process stability when counting the fraction defective (or in many healthcare applications, the fraction meeting requirements). The p Chart works for most data sets.
However, if your data meets certain criteria, you may need to consider an XmR Chart or a Laney p' Chart (p Prime).
- Consider an XmR Chart if the denominator does not vary widely from sample to sample. And your p chart control limits seem too narrow for the data and most points are highlighted as unstable. See below example.
- Consider a Laney p' Chart (p Prime) if: the sample sizes in your denominator are large and vary greatly.
Compare a p chart to an XmR chart on the same data
The control limits on this p chart seem too narrow for the data and all points are considered unstable.
Here is an XmR Chart run on the same data:
Laney p' chart on the same data
A Laney p' Chart will have wider control limits than the p Chart and it will have varying control limits that may help identify unstable points not identified by the XmR Chart. Here is a Laney p' Chart of the same data.
Toggle Between p Chart and p' Chart:
Specifically offered after running a p Chart macro, you can toggle between a p Chart and a p' Chart by inputting either "False" (p Chart) or "True" (p' Chart):
Laney p' Chart Ready Made Template
QI Macros also contains a Laney p' Chart template. Open it by clicking QI Macros > Control Chart Templates > Attribute > p Chart to open up the p Chart template. Then click on the p' Chart Skyline tab at the bottom to open up the Laney p' Chart (p Prime) template.
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QI Macros Draws These Charts Too!