# VIF: Calculate variance inflation factor (VIF) from the result of lm.

## Description

To evaluate multicolinearity of multiple regression model, calculating the variance inflation factor (VIF) from the result of lm(). If VIF is more than 10, multicolinearity is strongly suggested.

## Arguments

X

The object with class "lm", which would be generated by lm().

## Value

A variance inflation factor is returned.

## Examples

# NOT RUN {
# the target multiple regression model
res <- lm(Ozone ~ Wind+Temp+Solar.R, data=airquality)
summary(res)
# checking multicolinearity for independent variables.
VIF(lm(Wind ~ Temp+Solar.R, data=airquality))
VIF(lm(Temp ~ Wind+Solar.R, data=airquality))
VIF(lm(Solar.R ~ Wind+Temp, data=airquality))
# }