[R] offset in gam and spatial scale of variables

Lucia Rueda lucia.rueda at ba.ieo.es
Thu May 20 15:20:52 CEST 2010


Thanks for the inputs. I talked to my coworker, who has been the one doing
the analysis. Perhaps I wasn't making myself clear about the “differences in
spatial scales”.  Here is what he says:

"The truth is that measuring scales (i.e all area related variable are
measured in m2) and spatial definition of initial cartography are
homogeneous among extracted variables. But all variables (ie. sum of the
total rocky bottom in the surrounding area) are computed for each different
integration areas (buffer) (i.e in an area of 40squaremeters around the
sample, in an area of 80m2, …).
The question is then if we can build a model that includes variables
measured at different buffers (for example a model that includes 3
variables:  1.-  the amount of rocky bottom in an area of 80m2 ; 2- the
amount of sandy bottom in an area of 200m2; and the mean depth calculated in
a surrounding area of 50m2) considering that each variable may be expressing
different ecological processes. I believe that if there is not an ecological
constrain in the interpretation of the variables (and their ecological
effect over the specie), including them in a model is correct, unless there
is not a mathematical constrain."

Also, about the spatial correlation I thought from what I've read so far
that I had to build the model and then check if there was spatial
correlation in the residuals since they are supposed to be i.i.d. And if it
turns out that they are then I have to do something about it like gamm, gee,
sar, car, etc.



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