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Table 6 Stratified models by level of education and median household income for the association between birth weight and traffic and land use variables in a study of singleton births in Eastern Massachusetts between 1996 and 2002

From: The effects of socioeconomic status and indices of physical environment on reduced birth weight and preterm births in Eastern Massachusetts

  Educational attainment
  Low (≤ 12 years) High (>12 years)
Model covariates* Change (in grams) 95% CI Change (in grams) 95% CI
Cumulative traffic density -0.7 -4.3, 3.0 -0.1 -1.9, 1.6
Distance to major highways 1.8 -1.3, 4.9 4.9 2.8, 7.0
% land use for recreation and conservation (open space) 0.3 -3.3, 3.8 5.5 3.1, 8.0
  Median Household Income by census tract†
 50% >50%
  Change (in grams) 95% CI Change (in grams) 95% CI
Cumulative traffic density -1.7 -4.6, 1.3 0.6 -1.3, 2.5
Distance to major highways 3.8 1.0, 6.5 4.1 1.5, 6.7
% land use for recreation and conservation (openspace) 4.4 1.0, 7.9 4.2 1.3, 7.1
  1. APNCU – adequacy of prenatal care utilization; CI – confidence interval; SD – standard deviation Models controlled additionally for race, APNCU, mother education and median household income by census tract (where necessary), mother age, gestational age, cigarette smoking during pregnancy, previous infant greater than 4000 grams, previous preterm birth, chronic or gestational conditions of mother, and year of birth.
  2. *The effect is for 1 SD change in distribution of log-transformed traffic exposures and 1 SD change in distribution of % open space by census tract.
  3. †Categories of median household income: below and above the median of the distribution of the variable