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Multicollinearity

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Multicollinearity

Detection

VIF (Variance Inflation Factor): VIFj=11−Rj2VIF_j = \frac{1}{1 - R_j^2} where Rj2R_j^2 is from regressing xjx_j on all other predictors.
  • VIF >5> 5: Moderate multicollinearity
  • VIF >10> 10: Severe multicollinearity (needs attention) Condition number: κ=λmax⁡/λmin⁡\kappa = \sqrt{\lambda_{\max}/\lambda_{\min}}. κ>30\kappa > 30 indicates serious multicollinearity.

Remedies

MethodDescription
Remove variablesDrop one of the correlated predictors
PCAReplace correlated predictors with principal components
Ridge regressionAdd λ∑βj2\lambda\sum\beta_j^2 penalty
Partial least squaresFind latent components that predict both X and y
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