[R-sig-ME] spatial correlation structures in multilevel models?

[Steven J. Pierce]

You might also try doing that model with WinBUGS. There are packages that
will help you move the data out to WinBUGS from R and then bring the results
back into R for post processing. 

Steven J. Pierce, Ph.D. 
Associate Director 
Center for Statistical Training & Consulting (CSTAT) 
Michigan State University 
E-mail: pierces1 at msu.edu 
Web: http://www.cstat.msu.edu 

-----Original Message-----
From: Malcolm Fairbrother [mailto:m.fairbrother at bristol.ac.uk] 
Sent: Monday, July 12, 2010 12:00 PM
To: r-sig-mixed-models at r-project.org
Subject: [R-sig-ME] spatial correlation structures in multilevel models?

Dear all,

I'm interested in fitting a three-level model where the 1st level units are
individuals, and the 2nd and 3rd levels are (nested) geographical units,
whose locations (centroids) are known. (The precise location of each
individual is not known--just the unit to which he/she belongs.) I'd like to
exploit the fact that the locations are known, since people in
neighbouring/nearby units should be more similar than people in units that
are distant from each other. To be specific, I'd like a given unit's random
intercept to be adjusted according to the data from nearby/neighbouring
units--especially for instances where I have few observations for a unit but
lots of observations for neighbouring units.

My understanding is that lme4 and MCMCglmm cannot do this, in the sense that
they cannot specify spatial correlation structures. Using these packages, at
most, some characteristic of a unit's location (e.g., latitude, distance
from X point) and/or some (weighted) characteristic of a unit's neighbour(s)
could be included as a fixed effect.

However, as I understand it, nlme can do this, using the "correlation"
argument (e.g., "correlation = corExp(form = ~ ...").

Is this correct? Will nlme adjust the random intercepts in such a way? And
would it be a problem that it's the higher-level units, not the lowest-level
units, for which I know the locations?

If I'm being over-ambitious/demanding here, no worries at all--I'm just
curious whether this is possible. I don't have the data yet.

Many thanks,
Malcolm


Dr Malcolm Fairbrother
Lecturer
School of Geographical Sciences
University of Bristol