Hello. I have a multi-type point pattern, a ppp object in spatstat, with
two types, cases and controls. About 2600 point altogether. Overall, about
2% are cases. All in a polygonal window. I'm interested in the spatially
varying relative risk of being a case rather than a control. I'm aware of
the relrisk() command in spatstat, and also the risk() command in the sparr
package, both of which take a ppp object as an argument. I've done it with
both. They yield essentially similar pixel images, except that the range of
the relative risk, as shown in the colored legend, is very different in the
two plots.
plot(relrisk(thin.ems.ppp, at = "pixels", weights = NULL, varcov = NULL,
relative=TRUE, adjust=1, edge=TRUE, diggle=TRUE, se=FALSE,
casecontrol=TRUE, case = "case"))
yields relative risks ranging from 0 to about 0.16
In contrast,
risk(thin.ems.ppp, log = FALSE, verbose = TRUE, doplot = TRUE)
yields an image with relative risks ranging from 0 to about 40.
I've read the documentation for the packages, but perhaps I am still
misunderstanding what each package means by "relative risk." Can anyone
comment?
Thanks
--Chris Ryan
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