Content by Donald J. Wheeler
Mon, 10/03/2022 - 12:03
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 nonconforming product, we have to make use of some…
Tue, 09/06/2022 - 12:03
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 often, been based on superstition.
Capability…
Mon, 08/01/2022 - 12:03
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 is categorical (i.e., treatment levels). In both of…
Mon, 07/11/2022 - 12:03
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 theory by 40 years, chaos theory provides a way to…
Mon, 06/06/2022 - 12:03
Many different approaches to process improvement are on offer today. An appreciation of the way each approach works is crucial to selecting an approach that will be effective. Here we look at the problem of production and consider how the different…
Mon, 05/02/2022 - 12:03
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 and lack-of-fit statistics as part of the output.…
Mon, 04/04/2022 - 12:03
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 complex descriptions of various acceptance sampling…
Mon, 03/07/2022 - 12:03
Last month we looked at analyzing observational data. Here we will consider experimental data and discover a weakness in the way they are obtained that can contribute to the problem of nonreproducible results.
Background
The discipline of…
Mon, 02/07/2022 - 12:03
Most of the world’s data are obtained as byproducts of operations. These observational data track what happens over time and have a structure that requires a different approach to analysis than that used for experimental data. An understanding of…
Mon, 01/03/2022 - 12:03
On the face of it, it seems to be impossible for skewed variables to add up to a normally distributed result. Yet both common experience and mathematical theory combine to show us that this does indeed happen. In fact it is a fundamental property of…
