I am looking at the spatial distribution of poor households in a region
comprising a gradient of urban-rural postcodes. The data are counts and
they fit a negative binomial distribution, rather than a poisson
I am applying DCluster (ver. 0.1-3, windows) and would be grateful for
advice on a few topics.
A) As I understand it the default setting is based on a poisson
distribution. This creates some not implausible clusters, but I wonder
whether I could set the opgam, so that it uses a negative binomial
distribution (for which I have the parameters for the ?disease?
variable; size and mu) or to use a bootstrap procedure instead. Some of
the internal functions, like opgam.iscluster.negbin, seem to support
this, but I am uncertain about how to incorporate them.
B) To reduce the multiple testing problem (Waller & Gotway 2004,
?Applied Spatial Statistics for Public Health Data?, Wiley, p.208) I
wonder whether to set radius to <50% of step size, e.g. 100m radius in a
300m grid, so that the smallest circles won't touch?
I am getting results with ?poisson? (almost everything becomes a cluster
- possibly because the sites are clumped and not randomly distributed)
and with ?permutation?, but wonders how the ?negbin? is used? Not like
> > Error in rnbinom(n, size, prob) : invalid arguments
4. Turnbull. Is Turnbull analysis possible in DCluster yet?. Some
references in the manual, but haven?t been able to locate it.
A) I am considering increasing the study area (p.t. working with 1262
postcode points) and wonder what the limits might be for a desktop pc. I
gather that the distance matrices (created by tripack or spdep) could be
a limiting factor? Would it be an idea to run this step first and once
the table is created run the cluster detection algorithm?
B) I wonder whether permutations always are superior to standard stats.
Distributions, and if not, then why not?
Best wishes, Jakob
GISc student (MSc)
Birkbeck, University of London
I am out of my office until next week. For this readon, I will not be
able to check the code in DCluster and answer your other question,
Jakob. Don't desperate!! :)
The only advice I can give yiou a the moment is to try to follow as
much as possible the code in the examples, although I am quite sure
that you have already done it. I remember some problems like those
that you described but I think I fixed them (or maybe not) for the