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The VIF measures :

  • A.Percentage of variance explained
  • B.Heteroscedasticity
  • C.Multicollinearity
  • D.Residual standard error

Answer: C

The VIF measures multicollinearity.

The variance inflation factor of a predictor is \(1/(1 - R_j^{2})\), where \(R_j^{2}\) comes from regressing that predictor on all the others. It shows how much the variance of its regression coefficient is inflated by its overlap with the other predictors. A VIF of 1 means no overlap; values above about 4 or 5 are usually taken as a warning, so SPM's VIF of 4.2 signals that it is strongly correlated with the other predictors, probably CCFT.

The proportion of variance explained is \(R^{2}\). Heteroscedasticity is unequal spread of the residuals, checked with residual plots or tests such as Breusch-Pagan. The residual standard error is the typical size of a residual. None of these is what VIF measures.

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