Quality eLine Newsletter
December 2004
Vol. 6, No. 12

Quality Quiz
from Professor Cleary

Answer: "A" is the correct response.

Click here for a more complete video explanation.

Determining that a distribution is normal can be tricky business. One method is the chi-squared (c2) test, as Ann has indicated. The data set below reflects a pattern that follows the normal distribution very closely. CHARTrunner has calculated the chi squared value using this formula:

As illustrated in the chart below, the c2 value is 1.4. CHARTrunner compared this value to a tabular c2 value to determine whether it is reasonable to accept the hypothesis that the data does follow a normal distribution (note: the confidence level is 95%--a concept that will be explained in the accompanying video). This conclusion is reasonable, since the data looks to follow the normal distribution shown in CHARTrunner.

To gain perspective on this concept, examine the chart below. It clearly does not seem to resemble a normal distribution. Again, CHARTrunner calculates the c2 value, but now it is much larger (20.98). The software verifies the obvious by illustrating that it “fails” the confidence test, so it cannot be assumed that the data follows a normal distribution.

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