Donald J. Wheeler
The computation for skewness does not fully describe everything that happens as a distribution becomes more skewed. Here we shall use some examples to visualize just what skewness does—and does not—...
Donald J. Wheeler
There are four major questions in statistics. These can be listed under the headings of description, probability, inference, and homogeneity. An appreciation of the relationships between these four...
Donald J. Wheeler
The cumulative sum (or Cusum) technique is occasionally offered as an alternative to process behavior charts, even though they have completely different objectives. Process behavior charts...
Donald J. Wheeler
Last month we found that capability and performance indexes have no inherent preference for one probability model over another. However, whenever we seek to convert these indexes into fractions of...
Donald J. Wheeler
Many people have been taught that capability indexes only apply to “normally distributed data.” This article will consider the various components of this idea to shed some light on what has, all too...
Donald J. Wheeler
The analysis of residuals is commonly recommended when fitting a regression equation to a data set. It has even been recommended for the analysis of experimental data where the independent variable...
Donald J. Wheeler
Walter Shewhart made a distinction between common causes and assignable causes based on the effects they have upon the process outcomes. While Shewhart’s distinction predated the arrival of chaos...
Donald J. Wheeler
Many different approaches to process improvement are on offer today. An appreciation of the way each approach works is crucial to selecting one that will be effective. Here we look at the problem of...
Donald J. Wheeler
Students are told that they need to check their data for normality before doing virtually any data analysis. And today’s software encourages this by automatically providing normal probability plots...
Donald J. Wheeler
Acceptance sampling uses the observed properties of a sample drawn from a lot or batch to make a decision about whether to accept or reject that lot or batch. Although the textbooks are full of...
