 # So, I need to determine multicollinearity of predictors, but I have only two. Sandra Terrell 2022-08-08 Answered
I need to determine multicollinearity of predictors, but I have only two. So, if VIF $\frac{1}{1-{R}_{j}^{2}}$ , then in case there are no other predictors VIF will always equal 1? So, maybe it's not even possible to gauge multicollinearity if there are only two predictors?
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Step 1
Let's say you have Y and two predictors ${X}_{1}$ and ${X}_{2}$ , then the ${R}_{j}^{2}$ in the VIF index is ${R}_{1}^{2}$ obtained from the model ${X}_{1}={\alpha }_{0}+{\alpha }_{1}{X}_{2}+\xi$ . That is, unless ${X}_{1}$ and ${X}_{2}$ are uncorrelated, ${R}_{1}^{2}>0$ , hence VIF $>1$ .

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