[R] warning associated with Logistic Regression

Guillem Chust chust at cict.fr
Sun Jan 25 14:59:07 CET 2004

Hi All,

When I tried to do logistic regression (with high maximum number of
iterations) I got the following warning message

Warning message:
fitted probabilities numerically 0 or 1 occurred in: (if
(is.empty.model(mt)) glm.fit.null else glm.fit)(x = X, y = Y,

As I checked from the Archive R-Help mails, it seems that this happens when
the dataset exhibits complete separation. However, p-values tend to 1, and
residual deviance tends to 0. My questions then is:
-Is the converged model correct? or
-Can I limit the number of iterations in order to avoid this warning? If I
do so, I’ve checked that the model selected by step can diverge in some
cases (I use 10 different presence-absence datasets and 18 explanatory
variables), and when I validate the model with independent data, the new
model is slightly more powerful (in the most part of cases).

Thanks in advance,

Guillem Chust

Guillem Chust 				       chust at cict.fr

Laboratoire Evolution et Diversité Biologique, UMR 5174 CNRS/UPS
UPS Toulouse III, batiment IVR3
118, route de Narbonne  - 31062 Toulouse Cedex 4, France
Tel 33 (0)5 61 55 67 58          Fax 33 (0)5 61 55 73 27

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