🎻 Comparing Many Groups

The grand finale. A t-test only ever compared two groups — so Block 4 opens the door to many. First, one-way ANOVA compares three or more group means in a single honest test using the F ratio. Then the course closes on two-way ANOVA: two factors at once, with the famous interaction that tells you when the effect of one thing depends on another — read straight off a single line graph.

By the end of Block 4 you can…

✓Compare three or more group means at once with a one-way ANOVA.
✓Read an F ratio and its degrees of freedom (df), and say what they mean.
✓Explain why ANOVA beats running many t-tests — the false-alarm risk piles up.
✓Read a two-way design for main effects AND the interaction.
✓Spot an interaction on a line graph — parallel lines mean none; crossing or fanning lines mean one.

Test yourself

Block 4 Practice Test

12 multiple-choice questions spanning Units 13–14 — one-way and two-way ANOVA, F ratios, df, and reading interactions. Practice only; never graded.

Sigma says: Don't memorize — reason. Count your groups first: two means a t-test, three or more means ANOVA. And on any two-way line graph, parallel lines mean no interaction. Half of statistics is just reading the picture in your head.