[R] smoothing splines and degrees of freedom

Spencer Graves spencer.graves at pdf.com
Thu Jun 29 16:36:02 CEST 2006

	  The help page for 'smooth.spline' says the argument 'df' is 'the 
desired equivalent number of degrees of freedom (trace of the smoother 
matrix).'  It also explains that the output of 'smooth.spline' includes 
a component 'fit', and two components of 'fit' are 'knot' and 'coef'. 
To learn more, you can run the examples, examine 'str(cars.spl)' and the 
other objects produced by those examples.  You can also read more in the 
references cited there.

	  If you would like further help from this group, please submit another 
question, preferably after first reading the posting guide! 
"www.R-project.org/posting-guide.html".  There is substantial but 
anecdotal evidence to suggest that posts more consistent with that guide 
tend to get better answers quicker.  For example, if the above does NOT 
answer your question, I believe you would have gotten a better reply if 
you had provided a simple, self-contained example, rather than having me 
rely on one from the 'example' section of the 'smooth.spline' help page.

	  Hope this helps.
	  Spencer Graves

Steven Shechter wrote:
> Hi,
> If I set df=2 in my smooth.spline function, is that equivalent to running
> a linear regression through my data?  It appears that df=# of data points
> gives the interpolating spline and that df = 2 gives the linear
> regression, but I just want to confirm this.
> Thank you,
> Steven
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