In Chapter 8, “The Difference between Two Means,” the t-test was the tool used to compare the means of two groups. However, if you need to test the means of more than two groups, the t-test can't handle the job because it is only defined for two groups. This chapter shows how to compare more than two means using the one-way analysis of variance, or anova for short. The F-test, which has made brief appearances in previous chapters, is the key element in an anova. It is the statistical tool necessary to compare many groups, just as the t-test compares two groups. This chapter also introduces multiple comparisons, reviews the topic of unequal variances, and extends nonparametric methods to the one-way layout.