Quality Quiz from Professor Cleary
Congratulations:
"A" is of course correct.
Click here for a more complete video explanation
"Variance between" is related to the central
limit theorem.
“Variance within” is essentially equal
to the average variance of the three samples (or in this case, the
three facilities).
Now we are ready to test the hypothesis that the three facilities are essentially the same.
Step 1:
(Interpretation for H0: Facilities
1, 2, and 3 are the same; this represents the null hypothesis.)
(Interpretation for H1: At
least one line is different from the others.)
Step 2:
Note: Walker again
got confused by the Alpha value and thought it had something to
do with the new Alfa Romeo Sportwagon that I have been dreaming
about.
Mike's Dream Car  Alfa Romeo 156 GTA Sportwagon
Step 3:
Calculate the statistical F
value by taking a ratio of the variance between to the variance
within, divided by the appropriate degrees of freedom.
Step 4:
Compare the calculated F value
to the tabular F value that you would find in the back
of a statistics textbook. For this case, the tabular F
value for an Alpha value of .05 is 3.68. In that, the calculated
F value (4.114) is greater than the tabular F
value (3.68), the null hypothesis is rejected. One can conclude
that at least one of the three facilities is different from the
others.
If your head feels as if it's full of cobwebs as you try to recall what you learned in Statistics 101, there's the alternative of using software programs to do these calculations for you.
Note: You may have
noticed a Pvalue of .038 on the printout, next to the F
value. What do you think this means? If you think that you know
the right answer, email me at mike@pqsystems.com. If your name is
drawn from all the correct answers submitted, you will win a copy
of DOEpack
EZ from PQ Systems, Inc.
Click here to register to win a free Quality Gamebox program.
Copyright 2006 PQ Systems.
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