opgam {DCluster}R Documentation

Openshaw's GAM

Description

Scan an area with Openshaw's Geographical Analysis Machine to look for clusters.

opgam is the main function, while gam.intern is called from there.

Usage

opgam(data, thegrid=NULL, radius=Inf, step=NULL,  alpha, iscluster=opgam.iscluster.default, set.idxorder=TRUE, ...)
opgam.intern(point, data, rr, set.idxorder, iscluster, alpha, ...)

Arguments

data A dataframe with the data, as described in DCluster manual page.
thegrid A two-columns matrix containing the points of the grid to be used. If it is null, a rectangular grid of step step is built.
radius The radius of the circles used in the computations.
step The step of the grid.
alpha Significance level of the tests performed.
iscluster Function used to decide whether the current circle is a possible cluster or not. It must have the same arguments and return the same object than gam.iscluster.default
set.idxorder Whether an index for the ordering by distance to the center of the current ball is calculated or not.
point Point where the curent ball is centred.
rr rr=radius*radius .
... Aditional arguments to be passed to iscluster.

Value

A dataframe with five columns:

x Easting coordinate of the center of the cluster.
y Northing coordinate of the center of the cluster.
statistic Value of the statistic computed.
cluster Is it a cluster (according to the criteria used)? It should be always TRUE.
pvalue Significance of the cluster.

References

Openshaw, S. and Charlton, M. and Wymer, C. and Craft, A. W. (1987). A mark I geographical analysis machine for the automated analysis of point data sets. International Journal of Geographical Information Systems 1, 335-358.

Waller, Lance A. and Turnbull, Bruce W. and Clarck, Larry C. and Nasca, Philip (1994). Spatial Pattern Analyses to Detect Rare Disease Clusters. In 'Case Studies in Biometry'. Chapter 1, 3-23.

See Also

DCluster, opgam.iscluster.default

Examples

library(spdep)

data(nc.sids)

sids<-data.frame(Observed=nc.sids$SID74)
sids<-cbind(sids, Expected=nc.sids$BIR74*sum(nc.sids$SID74)/sum(nc.sids$BIR74))
sids<-cbind(sids, x=nc.sids$x, y=nc.sids$y)

#GAM using the centroids of the areas in data
sidsgam<-opgam(data=sids,  radius=30, step=10, alpha=.002)

#Plot centroids
plot(sids$x, sids$y, xlab="Easting", ylab="Northing")
#Plot points marked as clusters
points(sidsgam$x, sidsgam$y, col="red", pch="*")


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