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Table 1 The social, housing and environmental variables considered. All factors were summarized at the census tract level for the two county study area.

From: Environmental and social determinants of human risk during a West Nile virus outbreak in the greater Chicago area, 2002

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