Hi,
For what you have said, it seems that the problem I encountered extends to 
selecting subsets of the area analysed. I assume that for selecting a subsample 
only the spatial weights of that subsample are to be computed and not for the 
whole area. Which means that if the subset is based on a non-geographical 
variable (i.e. lets say "% of higher degree"), the are would look like a gruyere 
cheese. Is that right?

Thanks,
Alfonso Echazarra




________________________________
De: Roger Bivand <Roger.Bivand@nhh.no>

CC: r-sig-geo@stat.math.ethz.ch
Enviado: mar,8 febrero, 2011 15:27
Asunto: Re: [R-sig-Geo] Using neighbours outside the area of analysis for 
constructing spatial weight matrices

On Tue, 8 Feb 2011, alfonso echazarra wrote:

> Hello,
> 
> I am constructing a spatial weight matrix and would like to use neighbours that 
>are not part ofthe area I am analysing. In this case, I am investigating crime 
>rates within Madrid and I would like to use Madrid's adjacent census tracts to 
>construct the spatial weights for census tracts on the edge of Madrid (queen 
>contiguity rule). Is that possible? Spatial weights matrices and dataset that 
>are analysed need to be of same size?
> 

With very few exceptions, they need to be of the same size. The exception is 
that localmoran.sad() and localmoran.exact() take a select= argument to select 
the zones to be tested, but even here the length of the nb object and the number 
of observations must agree - you just do not have to compute local Moran's I for 
all of the observations. My impression is that the distributional assumptions 
behind the tests would be affected if some of the x_j were omitted from 
computation but included in the spatial lags through w_{ij}. It may be possible 
to construct a lagged variable for inclusion in a regression, but I'm not sure 
whether this would address the edge effects you seem to be concerned about.

Roger

> 
> Thanks,
> Alfonso Echazarra
> 
> 
> 
> 
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> 
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-- Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand@nhh.no


      
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