[R-sig-eco] gam

[Bob O'Hara]

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
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