[R] unexpected GAM result - at least for me!

From: Monica Pisica <pisicandru_at_hotmail.com>
Date: Mon, 31 Mar 2008 12:34:22 +0000


I am afraid i am not understanding something very fundamental.... and does not matter how much i am looking into the book "Generalized Additive Models" of S. Wood i still don't understand my result.

I am trying to model presence / absence (presence = 1, absence = 0) of a species using some lidar metrics (i have 4 of these). I am using different models and such .... and when i used gam i got this very weird (for me) result which i thought it is not possible - or i have no idea how to interpret it.

> can3.gam <- gam(can>0~s(be)+s(crr)+s(ch)+s(home), family = 'binomial')
> summary(can3.gam)

Family: binomial
Link function: logit
can> 0 ~ s(be) + s(crr) + s(ch) + s(home) Parametric coefficients:

            Estimate Std. Error z value Pr(>|z|)
(Intercept)    85.39     162.88   0.524      0.6
Approximate significance of smooth terms:
          edf Est.rank Chi.sq p-value
s(be)   1.000        1  0.100   0.751
s(crr)  3.929        8  0.380   1.000
s(ch)   6.820        9  0.396   1.000
s(home) 1.000        1  0.314   0.575
R-sq.(adj) =      1   Deviance explained =  100%
UBRE score = -0.81413  Scale est. = 1         n = 148

Is this a perfect fit with no statistical significance, an over-estimating or what???? It seems that the significance of the smooths terms is "null". Of course with such a model i predict perfectly presence / absence of species.

Again, i hope you don't mind i'm asking you this. Any explanation will be very much appreciated.



PS. I've contacted the author of the book who is the package maintainer as well but until now i didn't get a reply.


R-help_at_r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Mon 31 Mar 2008 - 12:36:53 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Mon 31 Mar 2008 - 13:30:26 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.

list of date sections of archive