I am fitting a two dimensional smoother in gam, say junk =
gam(y~s(x1,x2)), to a response variable y that is always positive and
pretty well behaved, both x1 and x2 are contained within [0,1].

 

I then create a new dataset for prediction with values of (x1,x2) within
the range of the original data.

 

predict(junk,newdata,type="response")

 

My predicted values are a bit strange (some negative and some large
positive values).

 

When I plot the predicted surface, it looks well behaved with no strange
dips/etc.

 

Could it be a problem with the predict command? 

Is there a "safe" version of predict for higher-dimensional smoothers in
gam?

 

Elizabeth Johnson

Research Associate

Johns Hopkins Unviersity

Department of Biostatistics

 

 


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