[R] MGCV: Degrees of freedom of smooth terms

Christoph Scherber Christoph.Scherber at agr.uni-goettingen.de
Tue Jul 23 11:16:52 CEST 2013

Dear all,

This is just a quick question regarding degrees of freedom in GAM models fit by MGCV (using select=T):

Can I roughly interpret them as:

1 df: linear effect of x on y
2 df: approximately quadratic of x on y
3 df: approximately cubic effect of x on y?
1 df for a spatial term s(x,y): bilinear effect (?) or how would I call this?

And what does "ref.df" in the summary output mean; is this the unpenalized degrees of freedom for
each term?

Thank you very much for answering!

Best wishes,

PD Dr Christoph Scherber
Georg-August University Goettingen
Department of Crop Science
Grisebachstrasse 6
D-37077 Goettingen
phone 0049 (0)551 39 8807
fax 0049 (0)551 39 8806

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