Table 2 Association between altitude of residence and risk of hospitalisation for atopic childhood asthma (n = 33 808).

Model	RR (95% CI)	p Value
Univariate analysis
Altitude of residence (m)		0.151
<900	1.00
900–1199	0.89 (0.67 to 1.16)	0.383
⩾1200	1.25 (0.95 to 1.64)	0.105
Multivariate analysis
Altitude of residence (m)		<0.001
<900	1.00
900–1199	1.49 (1.05 to 2.11)	0.026
⩾1200	2.08 (1.45 to 2.98)	<0.001
per 100‐m increase	1.07 (1.01 to 1.12)	0.013
Multivariate analysis (winter hospitalisations for atopic asthma n = 68)
Altitude of residence (m)		0.041
<900	1
900–1199	1.71 (0.77 to 3.80)	0.188
⩾1200	2.33 (1.03 to 5.27)	0.042
Multivariate analysis (spring hospitalisations for atopic asthma n = 78)
Altitude of residence (m)		0.047
<900	1
900–1199	1.61 (0.82 to 3.16)	0.169
⩾1200	2.05 (1.01 to 4.16)	0.047
Multivariate analysis (summer hospitalisations for atopic asthma n = 68)
Altitude of residence (m)		0.034
<900	1
900–1199	1.36 (0.62 to 2.99)	0.441
⩾1200	2.22 (1.03 to 4.81)	0.043
Multivariate analysis (autumn hospitalisations for atopic asthma n = 91)
Altitude of residence (m)		0.047
<900	1
900–1199	1.36 (0.75 to 2.46)	0.026
⩾1200	1.87 (1.00 to 3.48)	0.049

RRs and 95% CIs were estimated from logistic regression analyses. The multivariate analyses were fitted with a forward‐stepwise selection procedure, allowing for all variables in table 1, and included the following variables: sex, living environment, neonatal admission to hospital, farming environment, lack of breast feeding, postnatal smoking and low birth weight.