[R] GWR modeling with dummy variables

[Roger Bivand]

Steve Friedman <friedman.steve <at> gmail.com> writes:

> 
> Hi everyone,
> 
> I'm working with a modest sized spatial database consisting of 1513 records
> and 50 variables.  Fourteen of these are dummy variables delineating
> regional planning councils.  I'm trying to understand how to integrate the
> dummy variables in the geographically weight regression model. I'm reading
> Fotheringham et.al. and see reference to using dummy variables, but I don't
> see an example ilustrating the procedure.  I also don't see an example in
> the spgwr.pdf files associated with the package.
> 
> If anyone has experience with this I'd certainly like to hear from you.

As you may know, so-called GWR models are severely subject to collinearity 
impacting local coefficients. 

In R, dummy variables are operationalised as factors, split out into the 
appropriate dummies within model functions from the formula argument. So just 
put the categorical variable (factor) in the RHS of the formula, and it will 
just happen. So gwr(y ~ regional_planning_councils + ..., ...) for gwr in the 
spgwr package will just work for factor regional_planning_councils with 14 
levels. 

The R-sig-geo list is more focused on this kind of question.

Roger


> 
> I'm using R-2.5.1 on a PC.
> 
> Thanks in advance.
> 
> Steve
> 
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