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Table 1 Characteristics of the subjects

From: Chronic effects of ambient air pollution on respiratory morbidities among Chinese children: a cross-sectional study in Hong Kong

  Boys (N = 1141) Girls (N = 1062)
LPD (n = 485) MPD (n = 393) HPD (n = 263) LPD (n = 428) MPD (n = 356) HPD (n = 278)
Demographic characteristics
Age (in year) (Mean, SD) 9.0 (0.7) 9.0 (0.7) 9.1 (0.7) 9.0 (0.7) 9.0 (0.7) 9.0 (0.7)
Blue-collar job of fathera (%) 61.4*** 84.5*** 79.8*** 54.9*** 80.6*** 81.3***
Born in Hong Kong (%) 92.4*** 77.6*** 86.7*** 93.7*** 75.3*** 86.0***
Personal & parental characteristics
Low birth weightb (%) 10.1 8.1 7.6 9.3 13.2 9.4
Breastfed (%) 27.8*** 47.5*** 26.6*** 27.8** 36.2** 17.6**
Parental asthma (%) 4.5 2.5 5.7 5.4 4.8 7.2
Parental allergy (%) 20.2** 13.5** 11.8** 18.5* 12.6* 20.1*
Active smoking (%) 0.2 1.3 0.8 0.0 0.0 0.0
Physical activityc (%) 41.9*** 29.3*** 38.8*** 39.3** 29.8** 30.6**
Member of team sports (%) 26.4*** 13.7*** 25.1*** 23.6* 17.2* 23.0*
More outdoorsd (%) 50.7 48.1 48.7 49.8 50.3 51.8
Playing with furry toys (%) 17.7* 16.8* 11.0* 45.6 42.7 48.2
Housing environmental characteristics
Mould (%) 24.3*** 21.1*** 12.9*** 22.9# 22.2# 16.5#
New furniture (%) 15.9 18.6 16.3 18.7 21.9 18.3
Pets (%) 14.8** 11.7** 21.3** 22.9*** 13.2*** 22.3***
Incense (%) 20.8* 29.0* 24.3* 17.5 20.5 20.9
Passive smoking (%) 16.5*** 29.5*** 24.0*** 17.8*** 35.1*** 30.9***
More-ventilated in summere (%) 63.1*** 74.8*** 65.4*** 61.9* 71.6* 69.4*
More-ventilated in wintere (%) 81.2*** 76.1*** 68.4*** 80.4*** 72.2*** 69.8***
  1. LPD: low-pollution district; MPD: moderate-pollution district; HPD: high-pollution district.
  2. #P < 0.10; *P < 0.05; **P < 0.01; ***P < 0.001.
  3. aIncluding service workers, shop sales workers, skilled workers, unskilled workers, and other kindred workers.
  4. bBirth weight less than 2500 g.
  5. cTaking part in sports and/or vigorous free play at least three times a week for at least 30 minutes each time.
  6. dIndicating that children who spent more hours per week outdoors than the median value for their respective district and gender.
  7. eReferring to open windows at night and the whole day during the summer/winter.