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 P-value 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.

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