Content by Donald J. Wheeler
Mon, 12/13/2021 - 12:03
Management requires prediction. However, when making predictions it is easy to torture the data until they surrender and tell you what you expect to hear. Even though this torture may be unintentional, it can keep you from hearing the story the data…
Mon, 11/08/2021 - 12:03
One of the most common questions about any production process is, “What is the fraction nonconforming?” Many different approaches have been used to answer this question. This article will compare the two most widely used approaches and define the…
Mon, 10/04/2021 - 12:03
First, let it be known that all charts for count-based data are charts for individual values. Regardless of whether we are working with a count or a rate, we obtain one value per time period and want to plot a point every time we get a value. This…
Tue, 09/07/2021 - 12:03
What do the shape statistics known as skewness and kurtosis tell us about our data? Last month we saw how the average and standard deviation define the balance point and radius of gyration for our data. Once we have these two quantities the…
Mon, 08/02/2021 - 12:03
Your software routinely gives you four descriptive statistics for your data: the average, the standard deviation, the skewness, and the kurtosis. Of these only the average is easy to understand. This article and the next illustrate what these…
Tue, 07/06/2021 - 12:03
Measurement error is ubiquitous. As a result, over the past 250 years, different areas of science and engineering have come up with many different ways to deal with the problem of measurement error. One approach to the problem of measurement error…
Tue, 06/01/2021 - 12:03
For more than 40 years it has been common to use the precision to tolerance ratio (P/T ratio) to compare the standard deviation of measurement error with the specified tolerance for a particular product. The purpose of this comparison being an…
Mon, 05/03/2021 - 12:03
In my article, “Tightened 100% Inspection” (Quality Digest, March 29, 2021), we found that the excess costs associated with tightened specification limits are generally prohibitive. Here we consider the question: “Under what conditions can we use…
Mon, 03/29/2021 - 12:03
Inspection sounds simple. Screen out the bad stuff and ship the good stuff. However, measurement error will always create problems of misclassification where good stuff is rejected, and bad stuff gets shipped. While guard-bands and tightened…
Mon, 01/11/2021 - 12:03
In part one we found the baseline portion of an XmR chart to be the best technique for identifying potential outliers among four tests with variable overall alpha levels. In this part we will look at tests which maintain a fixed overall alpha level…
