[R-sig-eco] gam
Bob O'Hara
bohara at senckenberg.de
Thu May 17 19:44:30 CEST 2012
On 05/17/2012 06:17 PM, Mahnaz Rabbaniha wrote:
> Dear all
>
> i have done GAM for data ( they are non- normal and i find regression
> between Sillaginidae with several hydrological factors),i done :
>
> [1] "depth" "temperature" "salinity" "Sillaginidae"
>
> > pairs(sc,panel=function(x,y){points(x,y);lines(lowess(x,y))})
>
>> model<-gam(Sillaginidae~s(temperature)+s(salinity)+s(depth))
> but i take this 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
>
>
> please help me what can i do? or what is meaning this sentence?
It means that you don't have a lot of different values for one of your
covariates. You can check which with
length(unique(depth))
length(unique(temperature))
length(unique(salinity))
Unless you have a lot of data, that the sensible thing to is probably to
fit a straight line rather than a smooth curve. The other thing to do is
to define the maximum flexibility of the curve, e.g.
model<-gam(Sillaginidae~s(temperature, k=6)+s(salinity)+s(depth))
I hope this helps.
Bob
--
Bob O'Hara
Biodiversity and Climate Research Centre
Senckenberganlage 25
D-60325 Frankfurt am Main,
Germany
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