Do not write to multiple lists at the same time - nobody not on both lists
will know whether the question has been answered.
Always provide simple reproducible code.
See below inline for answer:
On Sun, 20 Apr 2014, irum Amir wrote:
From: imirum_a...@hotmail.com
To: r-sig-...@r-project.org
Date: Sun, 20 Apr 2014 09:23:14 +0000
Subject: [R-sig-Epi] problem with nb2listw( ) command
Dear all I am using scottish lip cancer data, which contains the
columns of observed, expected, AFF(person at risk) and latitude and
longitude. i use the commands
nc<-combine.data.shapefile(data=scotland,shp=shp,dbf=dbf)
###CARBayes package
This function is rather confusing and probably not a good idea here - see
PS below.
W.nb<-poly2nb(nc=scotland,row.names=rownames(scotland)) ### spdep
package
> W.nb
Out put is
Neighbour
list object:
Number of
regions: 56
Number of
nonzero links: 234
Percentage
nonzero weights: 7.461735
Average
number of links: 4.178571
3 regions
with no links:
^^^^^^^^^^^^^^^^^^^^
Please always read the output you see - your use of poly2nb created three
no-neighbour regions,
6554 6655 6756
^^^^^^^^^^^^^^^^^^^^
these.
> col.W<-nb2listw(W.nb,style="B",zero.policy=TRUE)
You use zero.policy=TRUE to get round the problem you yourself created
here, but then forget to continue to do the same in print.listw() and
moranI.test().
If you really want regions with no neighbours, you must use
zero.policy=TRUE everwhere - because usually you are advised not to
generate such neighbour objects (the theoretical properties of tests etc.
were developed for graphs with all regions connected.
If you read ?set.ZeroPolicyOption in spdep, you can see how to set the
option to TRUE globally as an option for your current session. Only use
this if you understand the consequences and wish to accept the risk that
the methods do not behave as expected.
Hope this clarifies,
Roger
PS. The boundaries in the scot_BNG shapefile in rgdal (see examples in
readOGR) include small slivers securing contiguity across water (spotted
by Barry Rowlingson, derived from an unprojected shapefile on Lance
Waller's website), and the data you are trying to analyse. This is also
used in Bivand et al. (2013), see:
http://www.asdar-book.org/bundles2ed/die_bundle.zip, and:
http://www.asdar-book.org/book2ed/die_mod.R chunks 31-46.
> col.W
which gives out put
Error in
print.listw(list(style = "B", neighbours = list(c(5L, 9L, 19L : regions with
no neighbours found, use zero.policy=TRUEwhen i use the command
moranI.test(Observed~AFF+offset(log(Expected)),
as(nc, "data.frame"), "negbin", 999,
listw=col.W, n=length(W.nb), S0=Szero(col.W)
)
Moran's I test of
spatial autocorrelation
Type of boots.: parametric
Model used when sampling: Negative
Binomial
Number of simulations: 999
Statistic: NA
p-value : NA
please help if any body has an idea.
There were 50 or more warnings (use
warnings() to see the first 50)
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--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: roger.biv...@nhh.no
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