Dr. Wheeler
Donald J. Wheeler

Author

SPC Press

Dr. Wheeler is a fellow of both the American Statistical Association and the American Society for Quality who has taught more than 1,000 seminars in 17 countries on six continents. He welcomes your questions; you can contact him at djwheeler@spcpress.com.

Mon, 12/08/2025 - 12:03
The Heavy-Tailed Normal Answers to questions
Mon, 10/01/2012 - 13:38
I n my September column, I showed how the normal distribution is the distribution of maximum uncertainty. Now I will expand on that theme and answer the questions generated by that column. Last month I demonstrated that the middle 91 percent of the…
What They Forgot to Tell You About the Normal Distribution How the normal distribution has maximum uncertainty
Tue, 09/04/2012 - 16:03
There are two key aspects of the normal distribution that make it the central probability model in statistics. However, students seldom hear about these important aspects, and as a result they end up making many unnecessary mistakes. Read on to…
What Is Leptokurtophobia? And why does it matter?
Mon, 07/30/2012 - 13:17
Three years ago this month Quality Digest Daily published my column, “Do You Have Leptokurtophobia?” Based on the reaction to that column, it contained a message that was needed. In this column I would like to explain the symptoms of…
What Is the Precision to Tolerance Ratio? And does it define a good measurement system?
Thu, 07/05/2012 - 11:13
In a class last month I was asked to explain a number that occurs in some measurement system evaluations and which is known as the precision to tolerance ratio (P/T ratio). As I will show in this column, it turns out to be related to the capability…
Analysis Using Few Data, Part 1 Some of these batches are not like the others…
Mon, 06/04/2012 - 13:06
Editor--Part 2 of this article can be found here. In some industries a few test batches will be produced prior to going into production. When this happens, a critical question is: “Are all of the test batches alike?” With only one value per batch,…
When Do We Use Subgrouped Data? A problem with service-sector average charts
Mon, 04/30/2012 - 11:32
When the data come along one value at a time, we tend to put them on a chart for individual values (an XmR chart). Since virtually all business and managerial data occur one value at a time, the primary chart for service-sector data is the XmR chart…
When Should We Compute New Limits? How to use the limits to track the process
Mon, 04/02/2012 - 14:51
Last month in “Exact Answers to the Wrong Questions” we looked at how we can compute useful limits with as few as six to 10 values. In this column I would like to consider the question of how to use the limits on a process behavior chart to…
Exact Answers to the Wrong Questions Why statisticians still do not understand Shewhart
Fri, 03/02/2012 - 13:52
In a recent article that shall remain nameless, a statistician carefully worked out the exact answer to the wrong question. Then, based on this exact answer, he made an erroneous recommendation regarding the use of a process behavior chart for…
If It Ain’t Broke… Problems with narrowly defined projects
Mon, 01/30/2012 - 11:17
The objective of all improvement projects should be to improve the effectiveness, or the efficiency, of the core processes. Everything else should be secondary to this objective. If you improve the efficiency of a support process, or even a portion…
Lies, Damned Lies, and Teens Who Smoke While Driving A lack of context is essential to propaganda
Mon, 01/02/2012 - 15:56
I n my February 1996 Quality Digest column I discussed an article out of USA Today. Since that article provides a great example of how we need to filter out the noise whenever we attempt to interpret data, I have updated it for my column today. “…