[R] problem with logistic regression

Peter Dalgaard
Mon, 07 Feb 2005 18:01:23 -0000

Helene.Dryssens at eleves.polytech-lille.fr writes:

> Hi,
>
> we try to do a logistic regression with the function glm.
> But we notice that this function don't give the same results as the SAS
proc
> catmod (differents estimate given).
> We try to change the contrast on R system with:
> >
options(contrasts=c(unordered="contr.SAS",ordered="contr.poly"))
>
> We also try with brlr and logistf functions.
> Unfortunately, the estimate aren't still the same.

contr.SAS is something of a contradiction in terms since SAS does not
use the same type of contrast in all procedures. I believe PROC CATMOD
is using sum contrasts (contr.sum), whereas contr.SAS gives you
something similar to PROC GENMOD (last level set to zero).

--
   O__  ---- Peter Dalgaard             Blegdamsvej 3
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N
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~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907