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Donald J. Wheeler
Parts per million (ppm) is part of the language of Six Sigma. It pervades the sales pitch and is used in all sorts of computations as a measure of quality. Yet what are the rules of arithmetic and statistics that govern the computation and usage of parts per million? To discover the answers read…
Donald J. Wheeler
The first axiom of data analysis is: “No data have meaning apart from their context.” Yet we all encounter measures that have been dreamed up without regard for either context or use. This column gives a couple of the more egregious examples I have encountered over the years.
Kentucky Higher…
Patrick Runkel
Right now I’m enjoying my daily dose of morning joe. As the steam rises off the cup, the dark, rich liquid triggers a powerful enzyme cascade that jump-starts my brain and central nervous system, delivering potent glints of perspicacity into the dark crevices of my still-dormant consciousness.…
CorDEX Instruments
NFPA 70E, full title “NFPA 70E—“Standard for Electrical Safety in the Workplace,” is a standard written by the National Fire Protection Association (NFPA). NFPA 70E was created primarily to assist companies and their personnel in avoiding potential fatalities and injuries from electrocution, arc-…
Dawn Keller
Juvenile idiopathic scoliosis. That was the diagnosis given to my then 8-year-old daughter last January. In short, it means that she’s young (under 10), she exhibits an abnormal amount of spinal curvature, and there’s no identified cause (aside from some bad luck).
Emilia’s X-rays indicated an S-…
Donald J. Wheeler
Author clarification--3/5/2015:It appears that I somewhat overstated my case in this article. I had forgotten that there are some families of distributions where we can estimate the shape of a probability model using the statistics for location and/or dispersion. Because of this, these families get…
Joel Smith
I typically attend a few lean Six Sigma conferences each year, and at each there’s at least one session about compensating belts. There are any number of ideas for how to do so, but they commonly include systems that provide a percentage of savings as a portion of pay, or provide a bonus for…
Patrick Runkel
If you’re not a statistician, looking through statistical output can sometimes make you feel a like you’ve wandered into Alice in Wonderland. Suddenly, you find yourself in a fantastical world where strange and mysterious phantasms appear out of nowhere. For example, consider the T and P in your t…
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. Last month in part one we found that this doesn’t appreciably affect the performance of process behavior charts for location. This month we look at how skewed data…
Dawn Keller
I really can’t make this stuff up.
I wrote a post a couple of years ago titled: “How to Talk to Your Kids About... Quality Improvement,” in which I lamented about Community Hero Day in my daughter’s first-grade class and the need to explain to her why I wasn’t at the “community-hero level” of…
Joel Smith
On a recent vacation, I was unsuccessfully trying to reunite with my family outside a busy shopping mall and starting to get a little stressed. I was on a crowded sidewalk, in a busy city known for crime, and it was raining. I thought there was no way things could get more aggravating when…
Greg Fox
At the end of part one, aspiring statisticians Woodrow “Woody” Stem and August “Russell” Leaf, creators of the famed Stem-and-Leaf plot, were in bad shape. They had beaten each other statsless after an argument about the challenge given to them by their mentor, Dr. Histeaux Graham. That challenge…
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…
