To: r-help at stat.math.ethz.ch From: "Juli G. Pausas" <juli at ceam.es> Subject: [R] glm: offset in poisson Date: Thu, 16 Mar 0 12:52:49 +0000 (GMT) X-Info: Mail Test Period R-users, Can an offset term be included in a Poisson model? I get an error message when trying that:
r3o <- glm(tax ~ areal + offset(o), family=poisson)
Error in (if (is.empty.model(mt)) glm.fit.null else glm.fit)(x = X, y = Y, :
inner loop 1; can't correct step size
In addition: Warning message:
Step size truncated due to divergence in: (if (is.empty.model(mt))
glm.fit.null else glm.fit)(x = X, y = Y,
(this error message doesn't appear with family= gaussian)
Certainly, but the offset is on the scale of the log mean for the
Poisson, and the mean for the Gaussian, so I suspect you may have completely
inappropriate values of the offset. Here's an example from the
V&R3 on-line exercises (and answers):
library(MASS)
data(Insurance)
glm(Claims ~ District*Group*Age - District:Group:Age
+ offset(log(Holders)), data=Insurance, family=poisson)
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._