Walker Runn is quality manager
for Color in a Can, a paint processing company with facilities in three
states. He is pleased to be assigned to the plant that lies furthest from
company headquarters, hoping that a 'out of sight, out of mind '
sensibility will keep the home office from pestering him about things like
statistical process control, or getting more training to do his work, or a
host of other things that are pebbles in his shoe.
The company sends a vice president to audit his quality system each year,
but Walker has been able to sustain a faŤade of competence because the
vice presidents that the home office sends have generally known little
about statistical process control, so he 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, Walker Runn 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 he has
never done hypothesis testing himself, Walker finds that he must actually
skim the chapter to learn some terminology. A section entitled
'Differences between Means ' draws his 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, Walker copies the case from the text
book and inserts it into a PowerPoint presentation. The data includes the
Using DOEpack, Walker finds
that the t value is 3.4. 'Aha, ' he says. This demonstrates how
different the lines are from each other, he points out to Dan Druff, who
nods, and then asks Walker what the alpha value might be.
Oh-oh. 'Selecting the Alpha ' was in the part of the chapter that
Walker had not skimmed. The unfortunate connection that came to his mind
derived from the sports car his neighbor just bought, an Alfa Romeo.
Fishing for a response, he blurted out '25, ' since the biggest (most
dominant) number in the formula was derived by adding the two X-bars
together. Not fancy, but fast calculation, he thought to himself.
Was Dan Druff impressed?