The Laney P Chart or P Prime Chart is an alternative to the standard P chart when over or underdispersion is in the data. We’ll include articles and videos covering its use.

We’ll start with a brief overview of the Chart, an explanation of over and underdispersion and follow with a video of the chart’s implementation in Minitab including how to test for over and underdispersion using an example. Then we include how to implement the Laney Charts in SigmaXL.

Next we’ll include a technical paper evaluating the performance of the Laney P Chart.

Then we’ll include a master’s thesis focusing on using Six Sigma to improve induction furnace efficiency. The thesis uses the Laney P Chart to reach conclusions.

We’ll conclude with

  • Laney’s Original ASQ Presentation
  • A Short Article from Laney
  • Laney’s Scientific Contributions

NOTE: Photo courtesy Minitab.


Brief Overview of the Laney P Chart

You can access the overview here.

Overdispersion and Unde Dispersion Explained


Video Discussion of Over and Underdispersion, Test for Discovering Them, and Implementation of the P Prime Chart in Minitab

You can watch the video from Knowledge Factory-Lean Six Sigma here.


Implementing Laney P and U Charts in SigmaXL: A Video from SigmaXL

You can watch the video here.


Evaluation of Laney P Prime Chart Performance


“Evaluation of Laney p’ Chart Performance”  by authors Muhammad Ahsan, Muhammad Mashuri and Hidayatul Khusna

 Their conclusion:

Finally, for large sample size, the p chart becomes extremely oversensitive and cannot be used to monitor the process, while the p’ chart gives realistic results. Based on the exploration of p and p’ charts, it is recommended to use p’ chart when the sample size is medium and large for a different number of subgroups. However, for same sample size, there are no significant differences between the p and the p’ charts, so using both of them is reasonable.

You can read the paper here.


Use of Laney p chart in a Six Sigma Project


In a  master’s thesis titled “Six Sigma–DMAIC Approach for Improving Induction Furnace Efficiency

and Output at an Iron Foundry Plant” author Chen Kwang Fong uses the Laney p chart.

In his thesis, Chen states:

Furthermore, Laney P-chart in Minitab was preferred for analyzing attribute

data that has sample size difference greater than 25%. This is because over-

dispersion happens when the sample size difference is large enough to practically

drive the sampling variation to zero. As a result, the control limits in regular P-chart

will be too narrow and all points are likely to fall out of control


You can access Chen’s thesis here.


David B. Laney’s ASQ Presentation from 2006

You can access the presentation here.


David P. Laney on the P’ Chart


This short article titled “P-Charts and U-Charts Work (But Only Sometimes)” appeared in the September 2007 Quality Digest and was written by David B. Laney. In it he explains the use of the chart.

You can read the short article here.


David B. Laney Scientific Contributions


David B. Laney unfortunately passed away November 25, 2021.

Copy and paste the following link into your browser for a list of David Laney’s Scientific Contributions.



Want to progress further with your Six Sigma career?

Join ISSSP today and access the hundreds of interviews, webinars, whitepapers, case studies, and other resources available in our online library.

Learn More Here