Between-Groups ANOVA. Chapter 12. When to use an F distribution Working with more than two samples ANOVA Used with two or more nominal independent variables and an interval dependent variable. Why not use multiple t -tests?. The problem of too many t tests Fishing for a finding
variance within groups
One-Way: hypothesis test including one nominal variable with more than two levels and a scale DV
Within-Groups: more than two samples, with the same participants; also called repeated-measures
Between-Groups: more than two samples, with different participants in each sample
Random selection of samples
Normally distributed sample
Homoscedasticity: samples come from populations with the same variance
Here the F statistic is 8.27 while the cutoff is 3.86. Do we reject the null hypothesis?
Step 1. Compare the variance (MS) by diving the sum squares by the degrees of freedom.
Step 2. Divide the between-groups MS by the within-groups MS value.
Step 3. Compare the calculated F to the critical F (in Appendix B).
If calculated is bigger than critical, we have a significant difference between means
R2 is a common measure of effect size for ANOVAs.