Table 2

 Incidence (%) of wheeze or asthma between ages 9 and 17 in relation to active smoking during adolescence

Incident wheezeIncident wheeze without a coldIncidence of diagnosed asthma
% (n/N)*Adjusted IRR(95% CI)†% (n/N)*Adjusted IRR(95% CI)†% (n/N)*Adjusted IRR(95% CI)†
n, cases; N, total of exposed; IRR, incidence risk ratio; CI, confidence interval.
*Population comprises subjects without missing values for the outcome, exposure, and confounding variables.
†All models adjusted for sex, age, study centre, and duration of exposure to environmental tobacco smoke (ETS) at follow up (for further detail see Methods).
Active smoking during adolescence
    No8.4 (160/1907)3.2 (58/1805)1.6 (27/1739)
    Yes22.6 (222/983)2.30 (1.88 to 2.82)11.4 (98/859)2.76 (1.99 to 3.84)4.7 (37/780)2.56 (1.55 to 4.21)
Duration of active smoking (years)
    Never8.4 (160/1907)3.2 (58/1805)1.6 (27/1739)
    ⩽216.8 (65/388)1.82 (1.38 to 2.40)8.0 (28/351)2.13 (1.37 to 3.33)2.5 (8/323)1.43 (0.65 to 3.17)
    2–424.3 (102/419)2.45 (1.92 to 3.11)10.7 (38/355)2.55 (1.69 to 3.85)5.7 (19/331)3.11 (1.71 to 5.65)
    >431.6 (49/155)3.10 (2.32 to 4.15)22.1 (30/136)4.95 (3.24 to 7.57)7.3 (8/110)3.97 (1.84 to 8.57)
Intensity of active smoking
    Never8.4 (160/1907)3.2 (58/1805)1.6 (27/1739)
    Occasionally14.3 (24/168)1.58 (1.06 to 2.36)7.7 (12/156)2.13 (1.17 to 3.87)2.7 (4/146)1.63 (0.58 to 4.58)
    Daily ⩽10 cigs19.5 (85/435)2.13 (1.66 to 2.74)9.3 (36/386)2.42 (1.61 to 3.64)4.3 (15/352)2.46 (1.31 to 4.63)
    Daily >10 cigs29.7 (111/374)2.95 (2.31 to 3.77)16.0 (50/313)3.66 (2.47 to 5.43)6.5 (18/278)3.34 (1.80 to 6.19)