what is vif used for 
vif measures the strength of the correlation between the independent variables in regression analysis this correlation is known as multicollinearity which can cause problems for regression models the bottom linewhile a moderate amount of multicollinearity is acceptable in a regression model a higher multicollinearity can be a cause for concern two measures can be taken to correct high multicollinearity first one or more of the highly correlated variables can be removed as the information provided by these variables is redundant the second method is to use principal components analysis or partial least square regression instead of ols regression which can respectively reduce the variables to a smaller set with no correlation or create new uncorrelated variables this will improve the predictability of a model 1