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

Data Snooping, Part 2 What pitfalls lurk outside your database?

Mon, 09/10/2018 - 12:03

In “Data Snooping Part 1” (Quality Digest, Aug. 6, 2018) we discovered the basis for the first caveat of data snooping. Here we discover three additional caveats of data snooping. Last month we discovered: Here we will use the data set from Part…

Data Snooping, Part 1 What pitfalls lurk within your database?

Mon, 08/06/2018 - 12:03

Data mining is the foundation for the current fad of “big data.” Today’s software makes it possible to look for all kinds of relationships among the variables contained in a database. But owning a pick and shovel will not do you much good if you do…

Enumerative and Analytic Studies Description vs. prediction

Mon, 07/16/2018 - 12:03

The ultimate purpose for collecting data is to take action. In some cases the action taken will depend upon a description of what is at hand. In others the action taken will depend upon a prediction of what will be. The use of data in support of…

Invisible Probability Models The gap between computations and reality

Mon, 06/04/2018 - 12:03

Some properties of a probability model are hard to describe in practical terms. The explanation for this rests upon the fact that most probability models will have both visible and invisible portions. Understanding how to work with these two…

The ‘Think System’ for Improvement First you guess what the problem might be…

Mon, 05/07/2018 - 12:03

In The Music Man, the con man Prof. Harold Hill sells band instruments and uniforms and then tells the kids that they can play music if they will “just think about the notes and then play them.” In many ways this “think system” is similar to what…

Is There an Empirical Rule for Probability Models? What do distributions have in common?

Mon, 04/02/2018 - 12:03

Last month we looked at what the empirical rule tells us about the data in a histogram. This month we will consider if there are any commonalities between different probability models that will allow us to make categorical statements without having…

The Empirical Rule What the average and standard deviation tell you about your histogram

Mon, 03/05/2018 - 12:03

How can we use descriptive statistics to characterize our data? When I was teaching at the University of Tennessee I found a curious statement in a textbook that offered a practical answer to this question. This statement was labeled as “the…

Is That Last Digit Really Significant? You no longer need to guess

Mon, 02/05/2018 - 12:03

Whenever we make a measurement, we have to decide how many digits to record. Traditional answers for this question are often little more than guesswork glorified by time. And with digital readouts, are all the displayed digits real? This column…

Honest Precision-to-Tolerance Ratios How to make sense of P/T ratios

Mon, 01/08/2018 - 12:03

The precision to tolerance ratio is commonly used to characterize the usefulness of a measurement system. While this ratio is appealingly simple, it overstates the damage due to measurement error. In this paper we show how to compute honest…

Capability Ratios Vary The key to using any number is to understand its limitations

Mon, 12/04/2017 - 12:03

Capability ratios are widely used and sometimes misunderstood. The computer will gladly offer up values of each of the commonly used capability and performance indexes. Yet there is little appreciation of the inherent uncertainty contained in each…