Vol. 10, No. 7 July 2008
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Quality Quiz from Professor Cleary

Clara Nett is quality manager for Color in a Can, a paint processing company with facilities in three states. She is pleased to be assigned to the plant that lies furthest from company headquarters, hoping that an 'out of sight, out of mind ' sensibility will keep the home office from pestering her about things like statistical process control, or getting more training to do her work, or a host of other things that are pebbles in her shoe.

The company sends a vice president to audit her quality system each year, but Clara has been able to sustain a facade of competence because the vice presidents that the home office sends have generally known little about statistical process control, so she can simply throw around a few impressive terms and charts and they leave satisfied. This time, however, the company has chosen to send Dan Druff, a highly competent (though somewhat flaky) statistician.

Thumbing through an old statistics textbook, Clara Nett decides that the only way to convince Dan Druff that the plant is producing consistently high quality paint is to wow him with hypothesis testing. Since she has never done hypothesis testing herself, Clara finds that she must actually skim the chapter to learn some terminology. A section entitled 'Differences between Means' draws her interest. In the associated case study, a plant has two identical production lines that produce identical products, not unlike the way Color in a Can is set up, with two lines that produce the same product.

To prepare for Dan Druff's visit, Clara copies the case from the text book and inserts it into a PowerPoint presentation. The data includes the following:

Book example

 Line 1 Line 2

Using DOEpack, Clara Nett finds that the calculated t value is 4.4. 'Aha, ' she says. This demonstrates how different the lines are from each other, she points out to Dan Druff, who nods, and then asks Clara what the alpha value might be.

Uh-oh.

'Selecting the Alpha ' was in the part of the chapter that Clara had not skimmed. The unfortunate connection that came to her mind derived from the sports car her neighbor just bought, an Alfa Romeo. Fishing for a response, she blurted out '35,' since the biggest (most dominant) number in the formula was derived by adding the two X-bars together. Not fancy, but fast calculation, she thought to herself.

Should Dan Druff be impressed by the wisdom of her answer?

A) yes

B) no