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Table 1 General characteristics of 45,562 study participantsa

From: Exposure to second-hand smoke during early life and subsequent sleep problems in children: a population-based cross-sectional study

Characteristics Overall Exposure to SHS during early life P value
Unexposed (n = 34,642) Ever exposed during pregnancy or the first 2 years of life (n = 4753) Ever exposed during both pregnancy and the first 2 years of life (n = 6167)
Child age, years 11.0 (2.6) 11.0 (2.6) 11.2 (2.6) 11.4 (2.5) < 0.01
Child sex
 Male 22,657 (49.7) 17,310 (50.0) 2382 (50.1) 2965 (48.1) 0.02
 Female 22,905 (50.3) 17,332 (50.0) 2371 (49.9) 3202 (51.9)  
Only child
 Yes 39,212 (86.1) 29,934 (86.4) 4067 (85.6) 5211 (84.5) < 0.01
 No 6350 (13.9) 4708 (13.6) 686 (14.4) 956 (15.5)  
Preterm birth
 Yes 2349 (5.2) 1660 (4.8) 300 (6.3) 389 (6.3) < 0.01
 No 43,213 (94.8) 32,982 (95.2) 4453 (93.7) 5778 (93.7)  
Low birth weight
 Yes 1777 (3.9) 1300 (3.8) 215 (4.5) 262 (4.2) < 0.01
 No 43,785 (96.1) 33,342 (96.2) 4538 (95.5) 5905 (95.8)  
Parental educational levels
 Low 29,113 (63.9) 21,146 (61.0) 3334 (70.1) 4633 (75.1) < 0.01
 High 16,449 (36.1) 13,496 (39.0) 1419 (29.9) 1534 (24.9)  
Yearly household income
  ≤ 10,000 Yuan 10,117 (22.2) 7393 (21.3) 1094 (23.0) 1630 (26.4) < 0.01
 10,001–30,000 Yuan 17,817 (39.1) 13,217 (38.2) 1970 (41.4) 2630 (42.6)  
 30,001–10,000 Yuan 15,346 (33.7) 12,156 (35.1) 1488 (31.3) 1702 (27.6)  
  > 100,000 Yuan 2282 (5.0) 1876 (5.4) 201 (4.2) 205 (3.3)  
Maternal age
  ≤ 25 years old 21,093 (46.3) 15,598 (45.0) 2391 (50.3) 3104 (50.3) < 0.01
 25–30 years old 20,376 (44.7) 16,063 (46.4) 1893 (39.8) 2420 (39.2)  
 30–35 years old 3002 (6.6) 2221 (6.4) 333 (7.0) 448 (7.3)  
 > 35 years old 1091 (2.4) 760 (2.2) 136 (2.9) 195 (3.2)  
Maternal smoking during pregnancy
 Yes 286 (0.6) 52 (0.2) 66 (1.4) 168 (2.7) < 0.01
 No 45,276 (99.4) 34,590 (99.8) 4687 (98.6) 5999 (97.3)  
Maternal alcohol consumption during pregnancy
 Yes 340 (0.7) 133 (0.4) 64 (1.3) 143 (2.3) < 0.01
 No 45,222 (99.3) 34,509 (99.6) 4689 (98.7) 6024 (97.7)  
  1. Abbreviation: SHS Second-hand smoke
  2. aData are mean (standard deviation) for continuous variables and number (percentage) for categorical variables