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, 04/07/2025 - 12:02
Sustaining Predictable and Economic Operation: What Does It Take?Entropy will make each and every process unpredictable
Mon, 11/06/2017 - 12:03
In theory, a production process is always predictable. In practice, however, predictable operation is an achievement that has to be sustained, which is easier said than done. Predictable operation means that the process is doing the best that it…
When Should We Use Extra Detection Rules?Using process behavior charts effectively
Mon, 10/09/2017 - 12:03
How do extra detection rules work to increase the sensitivity of a process behavior chart? What types of signals do they detect? Which detection rules should be used, and when should they be used in practice? For the answers read on. In 1931, …
ANOX: The Analysis of Individual ValuesA new test for homogeneity
Tue, 09/05/2017 - 12:03
Sometimes we use a chart for individual values and a moving range (an XmR chart) to assess the homogeneity of a finite data set. Since this is an "off-label" use for the XmR chart, we first consider the drawbacks associated with using a sequential…
Autocorrelated DataWhat does autocorrelation tell you about your process?
Mon, 08/07/2017 - 12:03
Last month I mentioned that we can put autocorrelated data on a process behavior chart. But what is autocorrelated data and what does it tell us about our processes? This article will use examples to answer both of these questions. Autocorrelation…
A History of the Chart for Individual ValuesThe ultimate in homogeneous subgroups
Mon, 07/10/2017 - 12:03
The simplest type of process behavior chart is the chart for individual values and a moving range. It allows us to plot a point every time we get a value, making it perfect for data that occur one value at a time. A brief history of this simple…
We All Have to Use Less Than Perfect Data And process behavior charts work better than you know with imperfect data
Mon, 06/05/2017 - 12:03
In their recent article, “We Do Need Good Measurements,” Professors Stefan H. Steiner and R. Jock MacKay take exception to two of my Quality Digest articles, “Don’t We Need Good Measurements?” and “The Intraclass Correlation Coefficient.” While we…
More Capability ConfusionA little algebra, done correctly, can take you to places that don’t exist
Mon, 05/01/2017 - 12:03
Here we take a serious look at some nonsensical ideas about capability ratios. Following a quick review of predictability and capability and a brief discussion of the traditional ways of characterizing capability and performance, we will consider…
An F-Test for the 21st CenturyNo one wants to use 100-year-old techniques!
Mon, 04/03/2017 - 12:03
A recent question from a statistician in Germany led me to the realization that the F-test of analysis of variance (ANOVA) fame is in serious need of an update. What the F-ratio does The F-ratio, created by Sir Ronald Fisher around 1925, is a…
The Three-Way ChartSome data structures need more than an average and range chart
Mon, 03/06/2017 - 12:03
The average and range chart handles most situations where the data can be logically organized into homogeneous subgroups. However, this chart breaks down when faced with a hierarchical data structure containing two or more levels of routine…
Don’t We Need Good Measurements? Process behavior charts work with imperfect data
Mon, 02/06/2017 - 11:03
Good measurements are like apple pie and motherhood. Who could ever be against having good measurements? Since we all want good measurements, it sounds reasonable when people are told to check out the quality of their measurement system before…