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Donald J. Wheeler
Whenever the original data pile up against a barrier or a boundary value, the histogram tends to be skewed and non-normal in shape. In 1967 Irving W. Burr computed the appropriate bias correction factors for non-normal probability models. These bias correction factors allow us to evaluate the…
Greg Fox
Greetings, fair reader. In the past, I've written several articles with practical tips related to Minitab graphs, such as how to discuss the sensitive issue of p-charts and Laney P' charts with your doctor; how to use a g-chart to monitor parenting success; and how to use a scatter plot to start…
John Flaig
Engineers have used safety margins for centuries to protect their companies and customers from the consequences of product degradation and failure. Sometimes the safety margins are fairly obvious (e.g., maximum-load limits posted in elevators), and other times they’re not.
Design margins are…
John Flaig
The claim is made and widely believed that C = 0 sampling plans are more cost effective than classic sampling plans such as ANSI/ASQ Z1.4. Below is a preliminary analysis of the cost difference between the two sampling plans using the hypergeometric probability distribution to compare a Squeglia C…
Dawn Keller
I spend the majority of my time entrenched in statistics. Using statistics. Studying statistics. Developing and testing statistical software. Statistics guide many of my decisions at work and in life. That’s the world of an engineer.
For this reason, you can imagine my surprise when my husband…
John Flaig
What’s wrong with root cause analysis? Let’s begin with the name, which is singular. It implies that there is only one root cause, when in reality most problems are usually caused by a complex combination of several factors, some of which are more significant than others.
To appreciate this point…
Donald J. Wheeler
In part one we found that the skewness and kurtosis parameters characterize the tails of a probability model rather than the central portion, and that because of this, probability models with the same shape parameters will only be similar in overall shape, not identical. However, since software…
