Quality eLine Newsletter
February 2004
Vol. 6, No. 2

Quality Quiz

This is the third quiz in a series of three that demonstrates how averages behave. Click below to view a brief video that reviews the first two quizzes from December and January.

See review video

Also, be sure to scroll to the end of the answer for a new video.

As we saw last month, the behavior of averages—like the behavior of animals—can be fascinating, especially to someone like Hartford Simsack, who, after all, has little life outside the elaborate wrought iron gates of Greer Grate & Gate.

Simsack’s manager, Ford D. Rivver, has asked him to train several new technicians in the use of statistical concepts. Considering that stability of processes is often emphasized, Simsack elects to begin the training by defining stability and going on to examine out-of-control tests. He does not fully understand these tests himself, but he has often heard it expressed that the best way to learn something is to teach it, so he’s game for this approach, presenting all there is to know about out-of-control tests. Or at least, all he knows about out-of-control tests.

One of the technicians, Perry Winkel, comes to Simsack two weeks later to show him a chart that has been generated in his lab. He points out that all the X-bars are not only within the control limits, but are also close to the mean ( ). The chart appears below:

“Yes,” says Simsack, “the X-bars are indeed within the control limits. Congratulations; your process is in control.”

A. He’s right, of course. After all, what are control limits for, if not to show when everything is in control?

B. He’s wrong. A situation that seems too good to be true, generally is.

Copyright 2004 PQ Systems.

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