Data Analysis with Microsoft Excel: Updated for Office 2007

354 Statistical Methods

2 Click F from the Table of Contents column. Review the material and

scroll to the bottom of the worksheet. See Figure 9-1.

Figure 9-1

The F

distribution

The F distribution has two degree-of-freedom parameters: the numerator

and denominator degrees of freedom. The distribution is usually referred to

as F(m, n)—that is, the F distribution with m numerator degrees of freedom

and n denominator degrees of freedom. The Distribution workbook opens

with an F(4,9) distribution.

Like the x^2 distribution, the F distribution is skewed. To help you better

understand the shape of the F distribution, the worksheet lets you vary the

degrees of freedom of the numerator and the denominator by clicking the

degrees-of-freedom scroll arrows. Experiment with the worksheet to view

how the distribution of F changes as you increase the degrees of freedom.

To increase the degrees of freedom in the numerator and

denominator:

1 Click the up spin arrow to increase the numerator degrees of freedom

to 10.

2 Click the up spin arrow to increase the denominator degrees of freedom

to 15. Then watch how the distribution changes.

In this book, hypothesis tests based on the F distribution always use the

area under the upper tail of the distribution to determine the p value.