Geographical information system and environmental epidemiology: a cross-sectional spatial analysis of the effects of traffic-related air pollution on population respiratory health

Table 2 Distribution of confounding factors by the distance classes in males and females.

	Males(n = 944)			Females(n = 1118)
	Distance of residence to main road			Distance of residence to main road
	<100 m	100-250 m	250-800 m	<100 m	100-250 m	250-800 m
	n = 263M	n = 279	n = 402	n = 322	n = 332	n = 464
	%	%	%	%	%	%
Age (years)
8-24	19.4	22.6	19.7	13.4*	16.9	18.1
25-64	56.7	60.9	58.7	55.5	61.4	58.0
65-97	19.9	16.5	21.6	31.1	21.7	23.9
Smoking habits
smokers	27.3	26.9	30.6	17.7	17.5	16.6
ex-smokers	43.4	39.8	39.3	17.7	16.2	16.6
non-smokers	29.3	33.3	30.1	64.6	66.3	66.8
Passive smoking exposure
yes	59.1	57.7	58.2	43.2 #	49.1	51.3
no	40.9	42.3	41.8	56.8	50.9	48.7
Educational level
low	41.1	45.2	42.3	65.5 #	57.8	56.9
medium	30.4	31.9	30.1	14.6	21.4	22.6
high	28.5	22.9	27.6	19.9	20.8	20.5
Work position
manager/white collar	13.7	17.9	19.2	8.9 *	16.7	13.7
blue collar/farmer	19.5	19.7	20.3	10.1	6.1	8.7
merchant/craftsman	17.6	15.4	12.0	9.5	6.4	8.7
unemployed	49.2	47.0	48.5	71.5	70.8	68.9
Occupational exposure
yes	57.0	59.5	57.7	26.4 #	25.9	32.3
no	43.0	40.5	42.3	73.6	74.1	67.7
Number of hours at home
≥ 15 h	41.1	37.6	39.3	74.2	71.1	69.8
< 15 h	58.9	62.4	60.7	25.8	28.9	30.2
Time of residence
< 5 years	14.2	10.8	11.0	11.6	8.1	11.2
≥ 5 years	85.8	89.2	89.0	88.4	91.9	88.8
Type of self-reported environmental contamination
traffic	92.4***	65.2	75.2	93.6 ***	74.8	78.5
other	7.6	34.8	24.8	6.4	25.2	21.5

*** p < 0.001, ** p < 0.01, * p < 0.05, # 0.05 < p < 0.1 (borderline) from Pearson chi-square test; comparison between subjects living at different distances from the main road, separately in males and in females

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