Pearson Correlation Coefficient
r = Σ((xi - x̄)(yi - ȳ)) / sqrt(Σ(xi - x̄)² × Σ(yi - ȳ)²)
Interpreting r Values
- |r| = 1.0: Perfect linear relationship
- 0.7 ≤ |r| < 1.0: Strong correlation
- 0.4 ≤ |r| < 0.7: Moderate correlation
- 0.2 ≤ |r| < 0.4: Weak correlation
- |r| < 0.2: Very weak or no correlation