Cuzick and Edwards (1990) first presented and analysed these data.
The data record 62 cases of childhood leukaemia and lymphoma
diagnosed in the North Humberside region of England between 1974 and
1986, together with 141 controls selected at random from the birth
register for the same period.
The data are represented as a marked point pattern,
with the points giving the spatial location of each individual's home address
(actually, the centroid for the postal code)
and the marks identifying cases and controls.
Coordinates are expressed in units of 100 metres, and the resolution is
100 metres. At this resolution, there are some duplicated points.
To determine which points are duplicates,
use duplicated.ppp
.
To remove the duplication, use unique.ppp
.
Two versions of the dataset are supplied, both containing the
same point coordinates, but using different windows.
The dataset humberside
has a polygonal window with 102 edges
which closely approximates the Humberside region,
while humberside.convex
has a convex 5-sided polygonal window
originally used by Diggle and Chetwynd (1991) and shown in
Figure 1 of that paper. (This pentagon has been modified slightly
from the original data, by shifting two vertices horizontally by 1 unit,
so that the pentagon contains all the data points.)