Statistical Analysis with Excel For Dummies, Third Edition by Joseph Schmuller

Author:Joseph Schmuller
Language: eng
Format: epub
Publisher: John Wiley and Sons, Inc.
Published: 2013-03-07T16:00:00+00:00

Figure 11-13: Two members of the F-distribution family.

It makes a difference which df is in the numerator and which df is in the denominator. The F-distribution for df = 9 and df = 14 is different from the F-distribution for df = 14 and df = 9. For example, the critical value in the latter case is 3.98, not 3.21.

Using F in conjunction with t

One use of the F-distribution is in conjunction with the t-test for independent samples. Before you do the t-test, you use F to help decide whether to assume equal variances or unequal variances in the samples.

In the equal variances t-test example I show you earlier, the standard deviations are 2.71 and 2.79. The variances are 7.34 and 7.78. The F-ratio of these variances is

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