Table 2 Descriptive statistics for birth weight, small for gestational age, and preterm births by quartiles of traffic variables, land use, and median household income among all singleton births born in Eastern Massachusetts between 1996 and 2002
Continuous variables (quartiles) | Mean birth weight (SD) | Small for gestational age N (%) | Preterm birth N (%) | Comparison group (≥ 37 weeks; ≥ 2500 grams) N (%) | ||||
|---|---|---|---|---|---|---|---|---|
Cumulative traffic density/1000 (vehicles-km) | Â | Â | Â | Â | Â | Â | Â | Â |
   ≤ 261.0 | 3469 | (539) | 9441 | 22.4 | 7187 | 21.7 | 89628 | 25.6 |
   > 261.0 – 704.6 | 3427 | (526) | 10398 | 24.7 | 8105 | 24.4 | 87756 | 25.0 |
   > 704.6 – 1602.0 | 3398 | (564) | 10944 | 26.0 | 8628 | 26.0 | 86674 | 24.7 |
   > 1602.0 | 3368 | (569) | 11256 | 26.7 | 9207 | 27.7 | 85785 | 24.5 |
   Missing (688) | 3413 | (560) | 70 | 0.2 | 57 | 0.2 | 561 | 0.2 |
Distance to primary highways (meters) | Â | Â | Â | Â | Â | Â | Â | Â |
   ≤ 1107 | 3398 | (555) | 11067 | 26.3 | 8460 | 25.5 | 86888 | 24.8 |
   > 1107 – 2150 | 3403 | (565) | 10741 | 25.5 | 8496 | 25.6 | 87196 | 24.9 |
   > 2150 – 3745 | 3413 | (563) | 10482 | 24.9 | 8422 | 25.4 | 87529 | 25.0 |
   > 3750 | 3448 | (554) | 9819 | 23.3 | 7806 | 23.5 | 88791 | 25.3 |
% land use for recreation and conservation (open space) | Â | Â | Â | Â | Â | Â | Â | Â |
   ≤ 4.0 | 3363 | (568) | 11184 | 26.6 | 8905 | 26.8 | 81668 | 23.3 |
   > 4.0 – 9.4 | 3403 | (567) | 10861 | 25.8 | 8711 | 26.3 | 86966 | 24.8 |
   > 9.4 – 17.8 | 3447 | (547) | 9658 | 22.9 | 7182 | 21.6 | 85787 | 24.5 |
   > 17.8 | 3458 | (546) | 9210 | 21.9 | 7328 | 22.1 | 87770 | 25.0 |
   Missing (10470) | 3319 | (597) | 1196 | 2.8 | 1058 | 3.2 | 8213 | 2.3 |
Median household income (in US $) | Â | Â | Â | Â | Â | Â | Â | Â |
   ≤ 46336 | 3303 | (581) | 12853 | 30.5 | 10736 | 32.4 | 83081 | 23.7 |
   > 46336 – 62773 | 3406 | (564) | 10984 | 26.1 | 8405 | 25.3 | 86917 | 24.8 |
   > 62773 – 78583 | 3467 | (547) | 9778 | 23.2 | 7253 | 21.9 | 89304 | 25.5 |
   > 78583 | 3486 | (526) | 8494 | 20.2 | 6790 | 20.5 | 91102 | 26.0 |