Intensity 187
would typically choose a class of parame tric models for the intensity, and test hypotheses about the
model parameters, as explained in Chapters 9 and 10.
When the covariate Z is the distance to a spatial pattern, an other useful statistic is Foxall’s J-
function [269], explained in Section 8.10 and available using Jfox.
Tests for a point source of elevated risk
An important problem in spatial epidemiology is to determine whether a point source of radiation
or pollution gave rise to elevated risk of disease. This is the special case of testing whether intensity
depends on a covariate, where the covariate Z is distance to the po int source. The tests described
above can be applied, but a better option is a ‘focused test’ or ‘point source ...