Moran I with Edge effect correction

Hi,
  This is very interesting. I would like to know a little bit more about
how to use glist=argument to reduce weights on observations selected as
members of an edge set and how to identify such members.
There isn't a simple answer, so each case would need to be guided by the 
analyst. If a concave hull is available, one could down-weight all links 
to observations in the set of members of the concave hull. If the 
observations have polygon support, one could mark all polygons with less 
that 100% internal shared boundaries (having an external boundary) for 
down-weighting. The down-weighting might be done by iterating over the 
links in the nb object to apply the downweighting factor to each link. 
There is a discussion of concave hulls on:

http://r.789695.n4.nabble.com/Concave-hull-td863710.html

example(nc.sids)
nn <- card(ncCR85_nb)
summary(nn)
nc.sids$nn <- factor(nn)
spplot(nc.sids, "nn", col.regions=rev(grey.colors(9)))

But your choice of weights style will have a major impact, so for binary 
weights, the low neighbour count observations are already down-weighted. 
The problem of up-weighted low neighbour count observations is most 
pressing for row-standardised weights, and there the glist= argument will 
not help. These topics are not well covered in the literature, I'm afraid.

Hope this helps,

Roger
 Thanks in advance.
Laurence

2012/8/25 Roger Bivand <Roger.Bivand at nhh.no>

On Thu, 23 Aug 2012, Kitty Lee wrote:

 Hi. I have some study areas that are very irregularly shaped. I wonder if
there is a way to adjust for edge effect in computing Moran's I or Geary C?

The typical approach would be through the weights matrix, depending on how
W is constructed. If you row-standardise, edge observations will be
stressed, but with binary weights they are less salient. You could also
intervene directly to reduce weights on observations selected as members of
an edge set, through the glist= argument in nb2listw().

Hope this helps,

Roger

Any leads would be really appreciated.

K.

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Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
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Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no