Donald J. Wheeler
In last month’s column, we looked at how process-hyphen-control algorithms work with a process that is subject to occasional upsets. This column will consider how they work with a well-behaved...
Donald J. Wheeler
Many articles and some textbooks describe process behavior charts as a manual technique for keeping a process on target. For example, in Norway the words used for SPC (statistical process control)...
Donald J. Wheeler
As we learned last month, the precision to tolerance ratio is a trigonometric function multiplied by a scalar constant. This means that it should never be interpreted as a proportion or percentage....
Donald J. Wheeler
A simple approach for quantifying measurement error that has been around for over 200 years has recently been packaged as a “Type 1 repeatability study.” This column considers various questions...
Donald J. Wheeler
Chunky data can distort your computations and result in an erroneous interpretation of your data. This column explains the signs of chunky data, outlines the nature of the problem that causes it, and...
Donald J. Wheeler
The keys to effective process behavior charts are rational sampling and rational subgrouping. As implied by the word rational, we must use our knowledge of the context to collect and organize data in...
Donald J. Wheeler
Ever since 1935 people have been trying to fine-tune Walter Shewhart’s simple but sophisticated process behavior chart. One of these embellishments is the use of two-sigma “warning” limits. This...
Donald J. Wheeler
As the foundations of modern science were being laid, the need for a model for the uncertainty in a measurement became apparent. Here we look at the development of the theory of measurement error and...
Donald J. Wheeler
In memory of Al Phadt, Ph.D.
This article is a reprint of a paper Al and I presented several years ago. It illustrates how the interpretation and visual display of data in their context can...
Donald J. Wheeler
The shape parameters for a probability model are called skewness and kurtosis. While skewness at least sounds like something we might understand, kurtosis simply sounds like jargon. Here we’ll use...
