[R] gam error

Gavin Simpson
Thu, 03 Jun 2010 13:10:59 -0000

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:

str(obj)

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

HTH

G

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

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