Correlation and Regression

$-1 \leq r \leq 1$. Positive: both increase. Negative: one increases as other decreases.

$|r|$ close to 1: strong. Close to 0: weak.

Calculate using GDC (formula in data booklet is complex).

$y = a + bx$ (least squares). Use GDC.

• Only use for interpolation (within data range).
• Extrapolation is unreliable.

$r^2$ gives the proportion of variation in $y$ explained by $x$.

If $r = 0.9$, then $r^2 = 0.81$ → 81% of variation explained.