Douglas Bates <[EMAIL PROTECTED]> writes: > Federico Gherardini wrote: > > > I'm trying to fit a glm model using family=poisson(link = > > "identity"). The problem is that the glm function fits a model with > > a negative intercept, which sounds like a nonsense to me, being the > > response a Poisson variable. > > Not really. The negative intercept is on the scale of the linear > predictor. The expected response, which is the exponential of the > linear predictor, is always positive.
Not when the link is "identity"...! However, in that case, sufficient extrapolation will always lead to negative values, unless the slope is exactly zero. Whether a negative value is a problem for the intercept depends on whether it corresponds to a relevant extrapolation of data. -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
