Content by Donald J. Wheeler
Phase Two Charts and Their Probability LimitsDo you know what really happens in phase two?
Mon, 11/04/2019 - 11:03
In the past two months we have looked at how three-sigma limits work with skewed data. This column finds the power functions for the probability limits of phase two charts with skewed probability models, and compares the trade-offs made by three-…
The Ability to Detect SignalsProcess behavior charts and skewed data
Mon, 10/07/2019 - 12:03
Last month I looked at how the fixed-width limits of a process behavior chart filter out virtually all of the routine variation regardless of the shape of the histogram. In this column I will look at how effectively these fixed-width limits detect…
The Normality MythBe careful where you get your information
Mon, 09/09/2019 - 12:03
The oldest myth about process behavior charts is the myth that they require “normally distributed data.” If you have ever heard this idea, or if you have ever taught this to others, then you need to read this article. While this myth dates back to…
Avoiding Bias Correction ConfusionWhen should we use the various bias correction factors?
Mon, 08/05/2019 - 12:03
Recently I have had several questions about which bias correction factors to use when working with industrial data. Some books use one formula, other books use another, and the software may use a third formula. Which one is right? This article will…
Analysis of Means TechniquesWhen 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 3Comparisons 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 2Do 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 1Practical 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 AssuranceIt 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 PlotsYour 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…