Hi Sergio, based on my understanding ( see Wood Generalized Additive Model) smoothing basis incorporates the intercept already, due to identifiable issues. Therefore the intercept is always specified and you don't need to specify. I guess that your m2 to model is simply not correct.
Hope it helps Anna Anna Freni Sterrantino Department of Statistics University of Bologna, Italy via Belle Arti 41, 40124 BO. ________________________________ Da: SAEC <sergio.es...@uach.cl> A: r-help@r-project.org Inviato: Giovedì 11 Ottobre 2012 0:22 Oggetto: [R] GAM without intercept Hi everybody, I am trying to fit a GAM model without intercept using library mgcv. However, the result has nothing to do with the observed data. In fact the predicted points are far from the predicted points obtained from the model with intercept. For example: #First I generate some simulated data: library(mgcv) x<-seq(0,10,length=100) y<-x^2+rnorm(100) #then I fit a gam model with and without intercept m1<-gam(y~s(x,k=10,bs='cs')) m2<-gam(y~s(x,k=10,bs='cs')-1) #and now I obtain predicted values for the interval 0-1 x1<-seq(0,10,0.1) y1<-predict(m1,newdata=list(x=x1)) y2<-predict(m2,newdata=list(x=x1)) #plotting predicted values plot(x,y,ylim=c(0,100)) lines(x1,y1,lwd=4,col='red') lines(x1,y2,lwd=4,col='blue') In this example you can see that the red line are the predicted points from the model with intercept which fit pretty good to the data, but the blue line (without intercept) is far from the observed points. Probably I missunderstanding some key elements in gam modelling or using incorrect syntaxis. I don't know what the problem is. Any ideas will be helpful. Sergio -- Sergio A. Estay Inst. Ciencias Ambientales y Evolutivas Universidad Austral de Chile Casilla 567, Valdivia, Chile Phone: 5663-293913 http://www.ciencias.uach.cl/instituto/ciencias_ambientales_evolutivas/academicos/sergio-estay.php -- View this message in context: http://r.789695.n4.nabble.com/GAM-without-intercept-tp4645786.html Sent from the R help mailing list archive at Nabble.com. [[alternative HTML version deleted]] ______________________________________________ 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. [[alternative HTML version deleted]]
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