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.

Thu, 01/29/2009 - 14:03

Analysis of Means Techniques When to use each of the six ANOM techniques

Mon, 07/08/2019 - 12:03

During the past three months James Beagle and I presented columns that made extensive use of analysis of means techniques. Since these techniques may be new to some, this column explains when to use each technique and where to find tables of the…

When Are Instruments Equivalent? Part 3 Comparisons using multiple standards

Mon, 06/10/2019 - 12:03

In Parts One and Two we defined the equivalence of instruments in terms of bias and measurement error based on studies using a single standard. Here we look at comparing instruments for differences in bias or differences in measurement error while…

When Are Instruments Equivalent? Part 2 Do the instruments have the same amount of measurement error?

Mon, 05/06/2019 - 12:03

Last month we provided an operational definition of when measurement systems are equivalent in terms of bias. Here we will look at comparing the within-instrument measurement error between two or more systems. Once again we must emphasize that it…

When Are Instruments Equivalent? Part 1 Practical answers to an age-old question

Mon, 04/08/2019 - 12:03

As soon as we have two or more instruments for measuring the same property the question of equivalence raises its head. This paper provides an operational definition of when two or more instruments are equivalent in practice. Churchill Eisenhart,…

The Keys to Quality Assurance It takes more than a good capability ratio

Mon, 03/04/2019 - 12:03

Managers the world over want to know if things are “in control.” This usually is taken to mean that the process is producing 100-percent conforming product, and to this end an emphasis is placed upon having a good capability or performance index.…

Problems With Bubble Plots Your computer may be lying to you

Wed, 02/06/2019 - 12:03

With the click of your mouse you can turn a list of values into a bubble plot. No thought or effort is required. Simply sit back and let the software gods do the heavy lifting of transforming your list of numbers into a fancy graph. What could…

What Is the Probability That Your Process Is Predictable? How to compute a p-value for your process behavior chart

Wed, 01/09/2019 - 12:03

Story update 1/15/2019: Thanks to the sharp eye of Dr. Stan Alekman, who spotted an inconsistent value in figure 2, I discovered an error in the program used to construct the table of critical values for the prediction ratio. I have now…

Which Chart to Use? Individual values or averages?

Mon, 12/03/2018 - 12:03

Process behavior charts are the interface between your data and your brain. But you have to begin by making a choice about which type of chart to use. You can either plot the individual values themselves, or you can organize your data into rational…

Data Snooping Part 4 How’s that classification scheme working out for you?

Thu, 11/08/2018 - 12:03

In Part One and Part Two of this series we discovered some caveats of data snooping. In Part Three we discovered how listening to the voice of the process differs from the model-based approach and how it also provides a way to understand when our…

Data Snooping, Part 3 What happens when we cannot write models for the data?

Mon, 10/01/2018 - 12:03

Parts One and Two of this series illustrated four problems with using a model-building approach when data snooping. This column will present an alternative approach for data snooping that is of proven utility. This approach is completely empirical…