Table 3 Associations between air pollution and the four-class asthma severity score per each increase of one IQR in air pollutant concentrations
Air pollutantFirst methodSecond method
NoOR (95% CI)NoOR (95% CI)
NO2
    Crude model2901.03 (0.84 to 1.25)3080.95 (0.77 to 1.18)
    Adjusted model*2281.01 (0.79 to 1.28)2470.92 (0.72 to 1.18)
SO2
    Crude model2551.25 (0.91 to 1.70)3081.81 (1.33 to 2.46)
    Adjusted model*2001.22 (0.84 to 1.78)2471.70 (1.19 to 2.44)
O3O3-8 h
    Crude model2102.56 (1.68 to 3.91)
    Adjusted model*1622.56 (1.58 to 4.14)
O3-daysO3-summer
    Crude model2892.22 (1.61 to 3.07)3081.57 (1.26 to 1.96)
    Adjusted model*2232.53 (1.69 to 3.79)2471.57 (1.22 to 2.03)
Adjusted three-pollutant models
O3 (O3-days/O3-summer)1842.74 (1.68 to 4.48)2471.85 (1.29 to 2.64)
SO21841.33 (0.85 to 2.11)2472.27 (1.39 to 3.70)
NO21840.94 (0.68 to 1.29)2470.99 (0.64 to 1.52)
  • OR given for one class difference in score and for an increase of one interquartile range (IQR) in average concentration (or 36 days for O3-days).

  • *Model adjusted for age, sex, smoking habits, occupational exposure and educational level.

  • 95% CI, 95% confidence interval; OR, odds ratio.

  • NO2, nitrogen dioxide; O3, ozone; SO2, sulphur dioxide.