Harish Jose
I’m looking at a topic in statistics. I’ve had a lot of feedback on one of my earlier posts on OC curves and how one can use them to generate a reliability/confidence statement based on sample size (...
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...
Alan Metzel
Almost seven years ago, Quality Digest presented a short article by Matthew Barsalou titled “A Worksheet for Ishikawa Diagrams.” At the time, I commented concerning enhancements that provide...
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—...
Tony Boobier
Does your use of probabilities confuse your audience? Sometimes even using numbers can be misleading. The notion of a 1-in-a-100-year flood doesn’t prevent the possibility of flooding occurring in...
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
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...
William A. Levinson
Quality-related data collection is useful, but statistics can also deliver misleading and even dysfunctional results when incomplete. This is often the case when information is collected only from...
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...
Paul Laughlin
As I started reading The Book of Why: The New Science of Cause and Effect, by Judea Pearl and Dana Mackenzie (Basic Books, 2018), I was reminded how often analysts trot out the bromide “correlation...
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...
Danielle Underferth
As municipalities clamor for a slice of President Biden’s $1.2 trillion infrastructure spending bill, one Johns Hopkins scientist is re-examining one of the basic elements of road-building:...
Scott A. Hindle
In 2010, new to the world of statistical process control (SPC), I was intrigued by Don Wheeler’s statement that “No data have meaning apart from their context” (from his book, Understanding...
