Statistics 5601 (Geyer, Spring 2006) Examples: Two-Way Layout


General Instructions

To do each example, just click the "Submit" button. You do not have to type in any R instructions or specify a dataset. That's already done for you.


Example 7.1 in Hollander and Wolfe.

External Data Entry

Enter a dataset URL :



Note: In the friedman.test function call the "groups" variable goes in front of the vertical bar and the "blocks" variable goes behind the vertical bar. We are looking for a "method" effect here so method goes in front of the bar.

The second analysis done by the aov function is the usual parametric procedure: two-way ANOVA. It produces P = 0.004084 for comparison with the Friedman P-value.

The first line tells R that player is to be treated as a factor, that is, as a non-numerical variable. If it were omitted, the ANOVA would be nonsense. For some reason friedman.test comes out the same if it is omitted.

We don't also have to tell R that method is a factor, because it automatically treats any non-numerical variable as a factor. If method had been designated by numerical codes, we would also need a statement like the first line for method.

If R were consistent, these two analyses would have similar syntax, but it isn't and they don't.

Warning: Do not omit the lines converting the categorical variables to R factor objects. At least don't omit them unless you are sure it won't make a difference.