Table 3 Prevalence rates (%) of potential risk factors for asthma onset among different birth cohorts

Active smoking

20.12

23.32

28.31

30.71

0.15

Passive smoking

51.89

43.18

39.58

35.93

<0.001

Paternal asthma

1.94

2.34

2.79

2.53

0.23

Paternal allergic rhinitis

6.79

5.75

5.72

4.59

0.22

Paternal atopic eczema

1.39

1.01

1.14

0.95

0.22

Maternal asthma

1.98

2.07

2.19

2.53

0.81

Maternal allergic rhinitis

5.84

5.65

5.18

3.61

0.08

Maternal atopic eczema

1.07

0.88

0.78

0.51

0.81