[R] glm.fit warning message

[Davies, Jonathan]

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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[R] interpolation and 3D plots

[Davies, Jonathan]

I've been told that you may be able to help.

I have a complex linear model with multiple two-way interaction terms. Is
there a way to view the interaction terms in a 3d plot equivalent to the S
functions:
 
 plan-interp(x,y,z)
 image(plan)

where x and y are my explanatory variables and z my response variable.

Thanks,

Jonatha Davies

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