[R] cross-validation with count-data

[Martin Wegmann]

Hello, 

possibly it is a stupid question but after few hours of trying and searching, 
perhaps I used the wrong key words, I decided to post it. 

I have the output of a glm() of count data (poisson).
I would like to get the prediction error (cross-validation).

cv.glm() does not work with poisson error family data. Or I have to transform 
the output error pred. in some way. 

are there method especially for glm() with different error families to receive 
the model goodness / the model badness?

thanks in advance, Martin