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

Table 1 Characteristics of the subjects

	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 father^a (%)	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 weight^b (%)	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 activity^c (%)	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 outdoors^d (%)	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 summer^e (%)	63.1^***	74.8^***	65.4^***	61.9^*	71.6^*	69.4^*
More-ventilated in winter^e (%)	81.2^***	76.1^***	68.4^***	80.4^***	72.2^***	69.8^***

LPD: low-pollution district; MPD: moderate-pollution district; HPD: high-pollution district.
^#P < 0.10; *P < 0.05; **P < 0.01; ***P < 0.001.
^aIncluding service workers, shop sales workers, skilled workers, unskilled workers, and other kindred workers.
^bBirth weight less than 2500 g.
^cTaking part in sports and/or vigorous free play at least three times a week for at least 30 minutes each time.
^dIndicating that children who spent more hours per week outdoors than the median value for their respective district and gender.
^eReferring to open windows at night and the whole day during the summer/winter.

ISSN: 1471-2458