Mon, 06/05/2023 - 12:03
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 a way that answers the interesting questions.…
Mon, 05/01/2023 - 12:03
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 column will consider the theoretical and practical…
Mon, 04/03/2023 - 12:03
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 discover its consequences.
The problem may be…
Mon, 03/06/2023 - 12:03
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 facilitate discovery. Al’s integrated approach is a classic…
Mon, 02/06/2023 - 12:03
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 some examples to visualize just what happens to a…
Mon, 01/09/2023 - 12:03
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—involve.
The mean for a probability model…
Mon, 12/05/2022 - 12:03
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 areas is essential for successful data analysis.…
Mon, 10/31/2022 - 12:03
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 characterize whether a process has been operated predictably…
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…
