[R] Gam() function in R

Simon Wood simon at stats.gla.ac.uk
Mon Dec 6 11:54:22 CET 2004

> I'm   a new user of R gam() function. I am wondering how do we decide on the
> smooth function to use?
> The general form is gam(y~s(x1,df=i)+s(x2,df=j).......)  , how do we decide
> on the degree freedom to use for each smoother, and if we shold apply
> smoother to each attribute?

I guess you are using gam() from package gam, in which case you probably 
need to look at the help file for step.gam. 

By default gam() in package mgcv estimates the appropriate degrees of 
freedom automatically as part of model estimation using generalized cross 
validation, (although there is an adjustable  upper limit on the range 
of degrees of freedom considered).

Package gss also has routines for fitting GAMs where the choise of df is 
fully automatic.


> Simon Wood simon at stats.gla.ac.uk        www.stats.gla.ac.uk/~simon/
>>  Department of Statistics, University of Glasgow, Glasgow, G12 8QQ
>>>   Direct telephone: (0)141 330 4530          Fax: (0)141 330 4814

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