Pearson's r measures the strength and direction of a linear relationship between two variables, on a scale from −1 (perfect negative) to +1 (perfect positive).
Pearson correlation coefficient
0
—
r²
0
Covariance
0
n (pairs)
0
x̄ / ȳ
—
Interpreting r
|r| < 0.1 — negligible
0.1 – 0.3 — weak
0.3 – 0.5 — moderate
0.5 – 0.7 — strong
0.7 – 0.9 — very strong
≥ 0.9 — extremely strong / near-perfect
Correlation does not imply causation. A high r only means the two variables move together linearly.