USE OF DENSITY EQUALIZING MAP PROJECTIONS (DEMP) IN THE ANALYSIS OF CHILDHOOD-CANCER IN 4 CALIFORNIA COUNTIES

In studying geographic disease distributions, one normally compares ra tes among arbitrarily defined geographic subareas (for example, census tracts), thereby sacrificing the geographic detail of the original da ta. The sparser the data, the larger the subareas must be in order to calculate stable rates. This dilemma is avoided with he technique of d ensity equalizing map projections (DEMP). Boundaries of geographic sub regions are adjusted to equalize population density over the entire st udy area. Case locations plotted on the transformed map should have a uniform distribution if the underlying disease rates are constant. The present report describes the application of the DEMP technique to 401 childhood cancer cases occurring between 1980 and 1988 in four Califo rnia counties, with the use of map files and population data for the 2 62 tracts of the 1980 census. A kth nearest neighbour analysis provide s strong evidence for geographic non-uniformity in tract rates (p<10(- 4)). No such effect is observed for artificial cases generated under t he assumption of constant rates. Work is in progress to repeat the ana lysis with improved population estimates derived from both 1980 and 19 90 census data. Final epidemiologic conclusions will be reported when that analysis is complete.