Vol. 10, No. 12

December 2008

PQ Systems

Am I dreaming?

Quality Quiz: With a video!

Data in everyday life

Six Sigma

Bytes and pieces

FYI: Current releases


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Quality Quiz from Professor Cleary

"C" is correct.

Click here for a more complete video explanation

Twenty five percent is generally cited as the proper percentage to use to determine whether control limits must be adjusted. This is not mathematically derived, but instead has become acceptable practice. The work cited in (A) is bogus, as is the 'well known simulation model;’ Shewhart did not address the 25%.

Not all statisticians agree on the 25% figure (do they ever agree on anything?).

To learn more about this concept, you can purchase Practical Tools for Continuous Improvement which explains this and other statistical applications, click here.

The chart below shows an application of the 25% rule using CHARTrunner. Both CHARTrunner and SQCpack allow the user to choose a percentage to apply to the data. For a 30-day free trial of CHARTrunner or SQCpack go to www.pqsystems.com.

Click here to register to win a free Quality Gamebox program.


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