On Wednesday 19 May 2010 15:29, Joris Meys wrote: > Could you specify the package you use? If it is mgcv, this one centers your > variables before applying the smooths. That's something to take into > account when comparing different models. --- er, actually it only centres variables in this way for some smoothing bases, for numerical stability purposes: but this is done in a way that is user transparent and makes absolutely no difference to model interpretation or comparison. Of course the smooths themselves are subject to `centering constraints' (but that's very different to centering the variables) --- these are just identifiability constraints --- all gam fitting packages have to put some identifiability constraints on the smooths, and the centering constraints used by `mgcv' and `gam' have the benefit of minimizing the standard errors on the constrained smooths.
best, Simon -- > Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK > +44 1225 386603 www.maths.bath.ac.uk/~sw283 ______________________________________________ R-help@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.
