[R] prediction, gam, mgcv

[gabriele.accetta@virgilio.it]

I fitted a GAM model with Poisson distribution
using the function gam() in the mgcv package.

My model is of the form:
mod<-gam(y~s(x0)+s(x1)+s(x2),family=poisson).


To extract estimates at a specified set of covariate
values I used the gam `predict' method. 

But I want to get
estimate and standard error of the difference of two fitted values.

Can someone explain what should I do?

Thank you
gabriele