Content by Donald J. Wheeler
Properties of Probability Models, Part 3 What they forgot to tell you about the lognormals
Mon, 10/05/2015 - 16:43
The best analysis is the simplest analysis that provides the needed insight. Of course this requires enough knowledge to strike a balance between the needed simplicity and unnecessary complexity. In parts one and two of this series we looked at the… Properties of Probability Models, Part 2What they forgot to tell you about the Gammas
Tue, 09/01/2015 - 15:53
Story update 9/8/2015: There was an error in the data set for columns "Skew" and "Kurt" in figure 7. The error has been corrected.
Clear thinking and simplicity of analysis require concise, clear, and correct notions about probability models and… Properties of Probability Models, Part 1What they forgot to tell you about Weibull distributions
Mon, 08/03/2015 - 17:04
Some commonly held ideas about skewed probability models are incorrect. These incorrect ideas are one source of complexity and confusion regarding the analysis of data. By examining the basic properties of skewed distributions this article can help… Rational Sampling More about the conceptual foundation of process behavior charts
Wed, 07/01/2015 - 17:03
While the computations for a process behavior chart are completely general and very robust, the secret to using a process behavior chart effectively lies in the art of rational sampling and rational subgrouping. Rational subgrouping was the topic… Rational SubgroupingThe conceptual foundation of process behavior charts
Mon, 06/01/2015 - 01:00
While the computations for a process behavior chart are completely general and very robust, the secret to using a process behavior chart effectively lies in the art of rational sampling and rational subgrouping. Rational subgrouping has to do with… The Parts-Per-Million ProblemWhen does a computation result in a number?
Mon, 05/11/2015 - 10:56
Parts per million (ppm) is part of the language of Six Sigma. It pervades the sales pitch and is used in all sorts of computations as a measure of quality. Yet what are the rules of arithmetic and statistics that govern the computation and usage of… Numerical JabberwockyNumbers that gyre and gymble in the wabe
Wed, 04/01/2015 - 16:40
The first axiom of data analysis is: “No data have meaning apart from their context.” Yet we all encounter measures that have been dreamed up without regard for either context or use. This column gives a couple of the more egregious examples I have… Probability LimitsA long standing controversy
Mon, 03/02/2015 - 13:04
Author clarification--3/5/2015:It appears that I somewhat overstated my case in this article. I had forgotten that there are some families of distributions where we can estimate the shape of a probability model using the statistics for location and/… Process Behavior Charts for Non-Normal Data, Part 2What happens to the range chart?
Tue, 02/03/2015 - 15:41
Whenever the original data pile up against a barrier or a boundary value, the histogram tends to be skewed and non-normal in shape. Last month in part one we found that this doesn’t appreciably affect the performance of process behavior charts for… Process Behavior Charts for Non-Normal Data, Part 1A guide for charts for location
Tue, 01/06/2015 - 15:24
Whenever the original data pile up against a barrier or a boundary value, the histogram tends to be skewed and non-normal in shape. In 1967 Irving W. Burr computed the appropriate bias correction factors for non-normal probability models. These…
