Compare three or more group means at once. F = between-group variance / within-group variance. Big F means the groups truly differ more than they wiggle internally.
Between SS—
Within SS—
F-statistic—
p-value—
Decision—
6.0
5.0
Two knobs, one F: push between up → groups separate more → F grows → reject H₀. Push within up → groups get noisier → F shrinks → harder to detect a difference even when one exists. ANOVA = signal-to-noise ratio.