Could you specify the package you use? If it is mgcv, this one centers your
variables before applying the smooths. That's something to take into account
when comparing different models.

In any way, If scales are too different, I try rescaling by either :
- expressing things in different units (meter versus kilometer, gram versus
kilogram)
- dividing by the standard deviation to get all variables appx on the same
order of magnitude. This does change the interpretation of your model
though.

But somehow I have the feeling you're not talking about that kind of
difference in scales. Could you please explain a bit more in detail what it
is exactly you're trying to do? I also suspect some autocorrelation problem,
which would direct you towards a gamm method.

Cheers
Joris

On Wed, May 19, 2010 at 10:37 AM, Lucia Rueda <lucia.rueda@ba.ieo.es> wrote:

>
> Hi,
>
> We are analizing the relationship between the abundance of groupers in line
> transects and some variables. We are using the quasipoisson distribution.
> Do
> we need to include the length of the transects as an offset if they all
> have
> the same length??
>
> Also, can we include in the gam models variables that are measured at
> different spatial scales? We have done an analysis to see what variables
> are
> better for different sizes of buffers around the transect lines and some
> variables are better at different scales. Can we run the gam model with
> several explanatory variables if they are measured at different spatial
> scales?
>
> Thanks,
>
> Lucia
> --
> View this message in context:
> http://r.789695.n4.nabble.com/offset-in-gam-and-spatial-scale-of-variables-tp2222483p2222483.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide
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>



-- 
Joris Meys
Statistical Consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

Coupure Links 653
B-9000 Gent

tel : +32 9 264 59 87
Joris.Meys@Ugent.be
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