Correlation: Definition

Correct Answer: Correlation

From the notes (Table 15 — Differences between correlation and regression):

• Correlation: Measure of association (relationship) between two variables. No cause-and-effect relationship. Symmetric: rxy = ryx. Range: −1 to +1. Coefficient is unit-free (pure number).

Types of Correlation (from notes)

1. Phenotypic correlation
2. Genetic correlation
3. Environmental correlation

Correlation Coefficient (r) Values

• r = +1 → Perfect positive correlation
• r = −1 → Perfect negative correlation
• r = 0 → No correlation

Contrast with Regression (from notes)

Regression = measure of change in one variable per unit change in another variable. Has a cause-and-effect relationship. NOT symmetric: bxy ≠ byx. Range: −∞ to +∞. Has units.