Leukemia clusters in upstate New York: how adding covariates changes the story

The 1978–1982 New York State TCE / Leukemia dataset is often used to test new cluster detection methodologies. We augment that dataset with demographic covariates from the 1980 census and find evidence that the relation between several of the TCE wastesites and elevated leukemia rates is probably confounded by the population's age and employment characteristics. This demonstrates a problem that is often mentioned, but seldom touched in detail–clustering can be related to covariates not directly related to the risks of interest.