From: Jordan T Watson <jordan2_at_u.washington.edu>

Date: Sat, 07 Apr 2007 21:57:31 -0700 (PDT)

g<-exp(f/4)

y<-rpois(rep(1,n),g)

Jordan Watson

School of Aquatic and Fishery Sciences

University of Washington

Seattle, WA

R-help_at_stat.math.ethz.ch 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 Sun 08 Apr 2007 - 05:02:34 GMT

Date: Sat, 07 Apr 2007 21:57:31 -0700 (PDT)

My data represent a similar pattern as below - where I see (seemingly) drastic changes in GCV for the poisson with different model structures, but the negative binomial often seems only to change in the second or third decimal place for the same models.

Is there a standard for how many decimals one should look at GCV, or am I totally missing something (I'm quite new to this, as I'm sure is obvious). Why such a difference in GCV change between poisson and negbin?

Thanks in advance!

Jordan

library(mgcv)

set.seed(0)

n<-400

sig<-2 x0 <- runif(n, 0, 1) x1 <- runif(n, 0, 1) x2 <- runif(n, 0, 1) x3 <- runif(n, 0, 1) f0 <- function(x) 2 * sin(pi * x) f1 <- function(x) exp(2 * x) f2 <- function(x) 0.2*x^11*(10*(1-x))^6+10*(10*x)^3*(1-x)^10f <- f0(x0) + f1(x1) + f2(x2)

g<-exp(f/4)

y<-rpois(rep(1,n),g)

summary(gam(y~s(x0)+s(x1)+s(x2)+s(x3),family=poisson,scale=-1))$gcv summary(gam(y~x0+x1+x2+s(x3),family=poisson,scale=-1))$gcv summary(gam(y~x0+x1+x2+x3,family=poisson,scale=-1))$gcv summary(gam(y~s(x3),family=poisson,scale=-1))$gcv summary(gam(y~s(x0)+s(x1)+s(x2)+s(x3),family=negative.binomial(1)))$gcv summary(gam(y~x0+x1+x2+s(x3),family=negative.binomial(1)))$gcvsummary(gam(y~x0+x1+x2+x3,family=negative.binomial(1)))$gcv summary(gam(y~s(x3),family=negative.binomial(1)))$gcv

Outputs from above:

> summary(gam(y~s(x0)+s(x1)+s(x2)+s(x3),family=poisson,scale=-1))$gcv

[1] 1.218529

> summary(gam(y~x0+x1+x2+s(x3),family=poisson,scale=-1))$gcv

[1] 5.058014

> summary(gam(y~x0+x1+x2+x3,family=poisson,scale=-1))$gcv

[1] 4.954163

> summary(gam(y~s(x3),family=poisson,scale=-1))$gcv

[1] 8.286693

*>
*

> summary(gam(y~s(x0)+s(x1)+s(x2)+s(x3),family=negative.binomial(1)))$gcv

[1] 1.047581

> summary(gam(y~x0+x1+x2+s(x3),family=negative.binomial(1)))$gcv

[1] 1.013617

> summary(gam(y~x0+x1+x2+x3,family=negative.binomial(1)))$gcv

[1] 1.012658

> summary(gam(y~s(x3),family=negative.binomial(1)))$gcv

[1] 1.005986

#######################################

Jordan Watson

School of Aquatic and Fishery Sciences

University of Washington

Seattle, WA

R-help_at_stat.math.ethz.ch 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 Sun 08 Apr 2007 - 05:02:34 GMT

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