Prevalence of asthma by environmental factors
| Environmental factor | Asthma prevalence % | ||
| 1974 | 1992 | 1998 | |
| Household smoking habits no. cigarettes·day−1 | |||
| 0–19 | 5.1 | 11.3 | 11.6 |
| 20–39 | 7.0 | 14.1 | 10.3 |
| >39 | 10.9 | 16.3 | 13.8 |
| Father' occupation level | |||
| Requiring university degree | 5.4 | 12.7 | 13.9 |
| Qualified, nonmanual | 5.8 | 11.6 | 12.7 |
| Manual | 5.4 | 10.7 | 10.3 |
| Number of persons in the household | |||
| ≥3 | 7.1 | 12.2 | 10.3 |
| 4–5 | 5.3 | 12.3 | 12.3 |
| ≤6 | 6.5 | 13.3 | 17.4 |
| Number of rooms in the house | |||
| 1–2 | 4.5 | 11.6 | 13.7 |
| 3–4 | 6.4 | 11.9 | 11.7 |
| ≥5 | 6.0 | 13.4 | 10.8 |
| Housing conditions | |||
| Central heating no damp rooms | 5.5 | 11.8 | 11.6 |
| No central heating or damp rooms | 6.8 | 13.3 | 19.7 |
| No central heating and damp rooms | 11.4 | 21.5 | 18.7 |
| Area of residence | |||
| A | 5.1 | 11.6 | 12.7 |
| B | 6.1 | 11.9 | 12.1 |
Urban area A: intensive housing, highbuildings, chemical industries, heavy traffic, scarce green areas (lower standard of living)
urban area B: lower and more widely spaced building, no chemical industries, light traffic, wide green areas (higher standard of living)
significant difference, p<0.05, Chi-squared test