Content by Donald J. Wheeler
Process Trial ChartsThe third of six uses for process behavior charts
Mon, 08/01/2016 - 15:37
Having described the report card chart and the process monitor chart in previous columns, we now turn to a third way that people use process behavior charts—the process trial chart. Here the emphasis shifts from the detection of unknown changes or… Process Monitor ChartsThe second of six uses of SPC (Corrected version of previous article)
Mon, 07/11/2016 - 13:36
Story update 10/9/2023: This article is a corrected version. The earlier version suffered from a programming error that affected all of the PID results.
Many articles and some textbooks describe process behavior charts as a manual technique for… Process Behavior Charts As Report CardsThe first of six uses
Mon, 06/06/2016 - 12:56
The simple process behavior chart can be used in many different ways. Since report card data are common in all types of businesses, the report card chart is often the first chart that people create. Some of the pros and cons of report card charts… Optimization and ExperimentationThe rest of the story…
Mon, 05/09/2016 - 15:55
Experimental designs that result in orthogonal data structures allow us to get the most out of both our analysis and our research budget. As a result, designed experiments have been used for everything from basic research to process optimization.… Useful HistogramsNo data have meaning apart from their context
Mon, 04/04/2016 - 10:31
Context involves both the background for the data and how the data behave. This behavior of the data is most easily seen by using two complementary graphs—the running record and the histogram. Here I address the secrets of creating useful histograms… Statistics 101 and Data Analysis: an ExampleThere may be a pop quiz on the secret foundation of statistical inference
Mon, 03/07/2016 - 15:49
Here we look at a simple example to discover the commonalties of various data analysis techniques widely used in industry today. Careful consideration of the following may result in insights that were not part of your introductory class in… The Levey-Jennings ChartHow to get the most out of your measurement system
Mon, 02/01/2016 - 10:43
The Levey-Jennings chart was created in the 1950s to answer questions about the quality and consistency of measurement systems in the chemical and process industries. This column will illustrate the fatal flaw in this technique and show a better… Statistical Tolerance IntervalsHow to make exact predictions
Mon, 01/04/2016 - 15:35
One computation that modern software offers to unsuspecting users is the statistical tolerance interval. Since this sounds very much like limits for individual values, some have been tempted to use them on process behavior charts in place of the… The Secret Foundation of Statistical InferenceWhat you don’t know can hurt you
Tue, 12/01/2015 - 15:14
When industrial classes in statistical techniques began to be taught by those without degrees in statistics it was inevitable that misunderstandings would abound and mythologies would proliferate. One of the things lost along the way was the secret… Shewhart and the Probability ApproachThe difference is much greater than how we compute the limits
Mon, 11/02/2015 - 14:39
In theory, there is no difference between theory and practice. In practice, there is. During the past three months we have looked at three families of probability models and found that they share some remarkable properties. These properties provide…
