I am feeling my way in the use of GLM's and have come across a warning whilst manually simplifying a model with interaction terms, removing terms one at a time from the maximum model (R1.9.0).

 

> model<-glm(midpnts~(AET+tempave+tempvar+MDE+sqrtarea)^2+Lat,family=poisson,weights=weightS)

> model2<-update(model,~.-tempave:tempvar)

Warning message: 

fitted rates numerically 0 occurred in: glm.fit(x = X, y = Y, weights = weights, start = start, etastart = etastart,

 

I have had limited success in interpreting this message, further when I use the STEP function [step(model)] the two way interaction term is removed from the model (along with several other interaction terms) and no warning message appears. I saw that there had previously been issue with the glm.fit function (in a much earlier version R 1.4.1), though I am more than ready to believe the problem lies with my data.

 

I would appreciate comments on whether the problem is with the data, and if so what is the interpretation of the warning message; finally, as the step function removes the interaction term in any case, can I continue the model simplification procedure from where the step function leaves me?

 

Thanks,

Jonathan


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