So, i was trying to improve mr LR model performing multiple linear regression on a dataset. I had a categorical variable region

Region(variable): Midwest Northeast South West

I made dummy variable for each of them and it did improved my model a bit.

Previous Model Summary enter image description here

After adding these variable(Which i made using a different variable) enter image description here

I am getting NA's in the coefficient for west, which i don't understand why. can someone explain?

  • $\begingroup$ Which tool / framework did you get these results with? Please add it to your post title and tags if possible. $\endgroup$ Jan 13, 2020 at 5:35
  • $\begingroup$ The output is from R studio $\endgroup$ Jan 13, 2020 at 21:16

1 Answer 1


You've given all four regions a dummy variable, so these are perfectly multicollinear, and the (unpenalized?) regression doesn't have a unique solution. R automatically drops a column in this situation and reports the NA.


(You can see where R calls C and subsequently FORTRAN functions, then inserts the NAs at
A nice article that helped me find that: http://madrury.github.io/jekyll/update/statistics/2016/07/20/lm-in-R.html )


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