Definition

Consider a Multiple Linear Regression model $y = X β + ϵ$ $V I F_{k} = \frac{1}{1 - R _{k}^{2}}, k = 1, 2, \dots, p - 1$ where $p - 1$ is the number of explanatory variables.

The variance inflation factor (VIF) measures how much the variance of an estimated regression coefficient is increased because of Multicollinearity