Table 1

The social, housing and environmental variables considered. All factors were summarized at the census tract level for the two county study area.

Variable
Description
Mean for all 1481 tracts in the study area

Population density
Housing units per square kilometer
2.02 units/square kilometer
Income
Median household income
$48,031
Race
Percentage of population that is white
54%
Age
Median age of population
33.7 years
Elevation
Mean elevation
192 meters above MSL

Elevation range
9.0 meters
Vegetation
Percentage vegetated
21.3%
Positive bird specimens
Meters from nearest positive bird
1965 meters
Housing age
Percentage of housing built 1940–1949
11.8%

Percentage of housing built 1950–1959
18.0%

Percentage of housing built 1940–1959
29.8%
Physiographic region
In the Chicago Lake Plain region or outside
Dummy variable
Mosquito Abatement District (MAD) status
In one of four MADs, DuPage County or outside of those areas
Dummy variables

Ruiz et al. International Journal of Health Geographics 2004 3:8   doi:10.1186/1476-072X-3-8