Table 1.

Kids Inpatient Database study sample description.

All births in 2000, 2003, and 2006	Median (IQR)	Unweighted N (%)
Birth weight (IQR), g	3324 (2976, 3656)	660,826
Low birth weight (n = 1,138,222)		431,725 (37.9%)
Preterm (n = 951,800)		218,500 (22.9%)
Total charges, 2005$	1603 (1058, 2647)	2,674,941
Total costs, 2005$	793 (527, 1283)	2,674,941
Length of stay, days	1.60 (1.11, 2.27)	2,543,584
Mean PM2.5, month of birth (µg/m3)	12.17 (9.29, 15.20)	319,506
Mean PM10, month of birth (µg/m3)	25.10 (19.43, 32.33)	278,428
Mean O3, month of birth (p.p.m.)	0.026 (0.017, 0.033)	272,282
Mean SO2, month of birth (p.p.m.)	0.0031 (0.0017, 0.0048)	213,981
Mean NO2, month of birth (p.p.b.)	0.017 (0.013, 0.024)	244,545
Mean CO, month of birth (p.p.m.)	0.58 (0.43, 0.77)	269,683
All births with available PM2.5, NO2, and CO data	Median (IQR)	Unweighted N (%)
Birth weight (IQR), g	3334 (2974, 3669)	68,953
Low birth weight		39,207 (37.0%)
Preterm (n = 75,878)		15,567 (26.9%)
Total charges, 2005 $	1855 (1203, 3271)	222,359
Total costs, 2005 $	996 (649, 1674)	222,359
Length of stay, days	1.64 (1.13, 2.45)	222,354
Mean PM2.5, month of birth (µg/m3)	12.63 (9.88, 15.91)	222,359
Mean PM10, month of birth (µg/m3)	26.31 (20.72, 34.00)	205,142
Mean O3, month of birth (p.p.m.)	0.025 (0.017, 0.032)	198,990
Mean SO2, month of birth (p.p.m.)	0.0032 (0.0017, 0.0051)	174,977
Mean NO2, month of birth (p.p.b.)	0.018 (0.013, 0.025)	222,359
Mean CO, month of birth (p.p.m.)	0.58 (0.45, 0.78)	222,359