[R] gam predictions with negbin model
Achim Zeileis
Achim.Zeileis at uibk.ac.at
Wed Oct 26 11:10:23 CEST 2011
On Wed, 26 Oct 2011, Kari Ruohonen wrote:
> Hi,
> I wonder if predict.gam is supposed to work with family=negbin() definition?
> It seems to me that the values returned by type="response" are far off the
> observed values. Here is an example output from the negbin examples:
>
>> set.seed(3)
>> n<-400
>> dat<-gamSim(1,n=n)
>> g<-exp(dat$f/5)
>> dat$y<-rnbinom(g,size=3,mu=g)
>> b<-gam(y~s(x0)+s(x1)+s(x2)+s(x3),family=negbin(3),data=dat)
>> summary(y)
> Min. 1st Qu. Median Mean 3rd Qu. Max.
> 0.6061 1.6340 2.8120 2.7970 3.9250 4.9830
>> summary(predict(b,type="response"))
> Min. 1st Qu. Median Mean 3rd Qu. Max.
> 0.8972 3.1610 4.8140 6.1170 8.1300 28.0100
>
> I.e. the range and mean of observed values (y)
What exactly is "y" in the code above? I guess you mean dat$y:
R> summary(dat$y)
Min. 1st Qu. Median Mean 3rd Qu. Max.
0.000 2.000 4.000 6.235 8.000 68.000
which looks rather reasonable...
Z
> are smaller than those of the
> predictions from the gam model. Should I somehow apply the estimated theta on
> these predictions?
>
> regards, Kari
>
> ______________________________________________
> 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.
>
More information about the R-help
mailing list