[R] gam error

Gavin Simpson gavin.simpson at ucl.ac.uk
Thu Jun 3 15:10:59 CEST 2010

On Thu, 2010-06-03 at 04:24 -0700, natalieh wrote:
> Hi all,
> I'm trying to use a gam (mgcv package) to analyse some data with a roughly U
> shaped curve. My model is very simple with just one explanatory variable:
> m1<-gam(CoT~s(incline))
> However I just keep getting the error message
> "Error in smooth.construct.tp.smooth.spec(object, dk$data, dk$knots) : 
>   A term has fewer unique covariate combinations than specified maximum
> degrees of freedom"

What this means is that you have fewer unique values for 'incline' than
you have knots in the spline. I forget now what the default (k = -1) in
function s() means, but it will be there in the help.

To set an upper limit, you could try:

K <- length(unique(incline)) - 1
m1 <- gam(CoT ~ s(incline, k = K))

Furthermore, you could try:


where 'obj' is/are your R data objects to check that R and you have the
same impression of what your data actually.



> Just wondering if anyone had come across this before/ could offer any advice
> on where the problem might lie
> Many thanks,
> Natalie

 Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
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