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Table 1 Characteristics of ASD Cases and Controls (interviewed information versus information from birth certificate)a

From: Air toxics and the risk of autism spectrum disorder: the results of a population based case–control study in southwestern Pennsylvania

  Interviewed Birth Certificate
Characteristic Cases (n = 217) Controls (n = 226) Cases (n = 216) Controls (n = 4,971)
  N (%) N (%) N (%) N (%)
Sex:     
 Male 169 (77.9) 175 (77.4) 168 (77.8) 3,980 (80.1)
 Female 48 (22.1) 51 (22.6) 48 (22.2) 991 (19.9)
Year of birth – n(%)     
 2005 43 (19.8) 53 (23.5) 43 (20.0) 1,153 (23.2)
 2006 59 (27.2) 44 (19.5) 59 (27.3) 1,151 (23.2)
 2007 48 (22.1) 46 (20.4) 48 (22.2) 1,066 (21.4)
 2008 37 (17.1) 41 (18.1) 36 (16.7) 888 (17.9)
 2009 30 (13.8) 42 (18.6) 30 (13.9) 713 (14.3)
County at birth – n(%)     
 Allegheny 131 (60.4) 133 (58.8) 129 (59.7) 2,883 (58.0)
 Armstrong 7 (3.2) 2 (0.9) 7 (3.2) 151 (3.0)
 Beaver 7 (3.2) 18 (8.0) 7 (3.2) 393 (7.9)
 Butler 17 (7.8) 19 (8.4) 18 (8.3) 409 (8.2)
 Washington 22 (10.1) 24 (10.6) 21 (9.7) 448 (9.0)
 Westmoreland 33 (15.2) 30 (13.3) 34 (15.7) 687 (13.8)
Maternal age (SD) – meanb 30.4(5.4) 31.8 (4.7) 30.4 (5.4) 28.5 (6.0)
Paternal age (SD) – mean2 32.6 (6.0) 33.6 (5.9) 32.8 (5.8) 31.4 (6.6)
Mother raced     
 White 194 (89.4) 219 (96.9) 196 (90.7) 4,055 (81.9)
 Black 15 (6.9) 4 (1.8) 16 (7.4) 692 (14.0)
 Other 2 (0.9) 2 (0.9) 4 (1.9) 205 (4.1)
Mother’s educatione     
  < High school graduate 3 (1.4) 2 (0.9) 6 (2.8) 475 (9.6)
 High school graduate and some college 95 (43.8) 46 (20.4) 92 (42.6) 2,536 (51.3)
  ≥ College graduate 119 (54.9) 178 (78.7) 118 (54.6) 1,937 (39.2)
Low birth weight (<2500 g)f,i (based on birth certificate) 23 (10.7) 9 (4.0) 23 (10.6) 341 (6.9)
Preterm birth (< 37 weeks)g,j (based on birth certificate) 31 (14.8) 20 (9.0) 31 (14.8) 514 (10.6)
Multiple births 18 (8.4) 9 (4.0) 18 (8.4) 189 (3.8)
Maternal Smoking during pregnancy or in 3 months prior to pregnancyh     
 Yes 54 (24.9) 24 (10.6) 30 (13.9) 1,165 (23.9)
 No 163 (75.1) 202 (89.4) 185 (86.0) 3,714 (76.1)
  1. aIncludes multiples births
  2. bMissing 2
  3. cMissing 632
  4. dMissing 19
  5. eMissing 23
  6. fMissing 13
  7. gMissing 119
  8. hMissing 92 controls and 1 case
  9. iMissing 1 case
  10. jMissing 4 cases and 6 controls
  11. Interview missing information