Use of density equalizing map projections (DEMP) in the analysis of childhood cancer in four California counties
In studying geographic disease distributions, one normally compares rates of arbitrarily defined geographic subareas (e.g. census tracts), thereby sacrificing the geographic detail of the original data. The sparser the data, the larger the subareas must be in order to calculate stable rates. This dilemma is avoided with the technique of Density Equalizing Map Projections (DEMP). Boundaries of geographic subregions are adjusted to equalize population density over the entire study area. Case locations plotted on the transformed map should have a uniform distribution if the underlying disease rates are constant. The density equalized map portrays both individual cases and rates, and can be understood by untrained observers. Simple statistical techniques can be used to test the uniformity of the transformed map. This report describes application of the DEMP technique to a sizeable `real-world` data set: 401 childhood cancer cases occurring between 1980 and 1988 in four California counties. In an earlier analysis of the same data, the California Department of Health Services (DHS) calculated rates for 101 communities and found no significant geographic variability. The DDS 1980--88 population estimates are no longer available, so in this analysis 1980 Census data were used; geographic units were 262 census tracts. A k`th nearest neighbor analysis, corrected for boundary effects and for within-tract variability, provides strong evidence for geographic nonuniformity in tract rates ({rho} < l0{sup {minus}4}). No such effect is observed for artificial cases generated under the assumption of constant rates. Pending reanalysis with 1980-88 population estimates, no epidemiologic conclusions can be drawn at this time.
- Research Organization:
- Lawrence Berkeley Lab., CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 73024
- Report Number(s):
- LBL--36630-Rev.; CONF-950168--1-Rev.; ON: DE95012388
- Country of Publication:
- United States
- Language:
- English
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Use of density equalizing map projections (DEMP) in the analysis of childhood cancer in four California counties