🔗 Relationships

Block 1 described one variable at a time. Now we look at pairs — what happens when two things move together. Correlation measures how tightly they track, in one number from −1 to +1. Regression goes one step further and draws the line that lets you predict one variable from the other.

By the end of Block 2 you can…

✓Compute and interpret Pearson r — read its sign for direction and its size for strength.
✓Read a scatterplot at a glance: uphill, downhill, or shapeless blob.
✓Know why correlation is not causation — a hidden third variable can drive both.
✓Find a regression line Ŷ = a + bX and use it to predict Y from any X.
✓Understand r² as the percent of variation one variable explains.

Test yourself

Block 2 Practice Test

12 multiple-choice questions spanning Units 6–7, with a few light calculations — just like the real thing. Practice only; never graded.

Sigma says: Don't memorize — reason. A correlation and its scatterplot always tell the same story, and r² is just r times itself. Picture the dot cloud and the rest falls into place.