Crude and adjusted prevalence of asthma symptoms and asthma diagnosis in three consecutive surveys according to parental reports and students answers to the ISAAC written questionnaire
| Health outcome | 1992–1993 | 1995–1997 | 1999–2000 | p‐value for trend | |||
| Crude | Adjusted | Crude | Adjusted | Crude | Adjusted | ||
| Parental questionnaire n | 1324 | 1668 | 1250 | ||||
| Wheeze ever | 20.9 | 19.9 (17.6–22.4) | 20.7 | 19.5 (17.4–21.7) | 25.2 | 22.5 (20.0–25.2) | 0.14 |
| Wheeze past year | 6.7 | 5.1 (4.0–6.6) | 6.8 | 5.0 (4.0–6.2) | 5.7 | 4.0 (0.3–5.2) | 0.15 |
| Wheeze after exercise | 9.1 | 7.8 (6.4–9.4) | 8.6 | 6.8 (5.6–8.2) | 8.3 | 7.4 (6.0–9.1) | 0.78 |
| Speech limiting wheeze | 1.4 | 0.9 (0.5–1.7) | 1.2 | 0.7 (0.4–1.2) | 1.4 | 0.7 (0.4–1.2) | 0.37 |
| Asthma ever | 9.7 | 7.8 (6.4–9.5) | 10.7 | 7.6 (6.4–9.1) | 10.3 | 7.4 (6.0–9.1) | 0.74 |
| Students' written questionnaire n | 1158 | 1386 | 1182 | ||||
| Wheeze ever | 18.5 | 17.8 (15.4–20.4) | 17.6 | 16.1 (14.0–18.3) | 20.4 | 16.6 (14.4–19.0) | 0.55 |
| Wheeze past year | 9.7 | 8.8 (7.2–10.8) | 9.2 | 7.3 (6.0–8.8) | 10.9 | 8.3 (6.8–10.1) | 0.83 |
| Wheeze after exercise | 18.9 | 19.3 (16.8–22.0) | 15.2 | 13.5 (11.5–15.6) | 18.5 | 16.8 (14.5–19.2) | 0.29 |
| Speech limiting wheeze | 2.2 | 1.5 (1.0–2.5) | 1.9 | 1.3 (0.8–2.0) | 2.4 | 1.6 (1.0–2.6) | 0.75 |
| Asthma ever | 10.8 | 9.6 (7.9–11.7) | 10.1 | 8.7 (7.2–10.5) | 12.3 | 9.6 (7.9–11.5) | 0.98 |
Data are presented as % or % (95% confidence interval) unless otherwise stated
Symptom rates were adjusted for study year, sex, parental education, study area, maternal and paternal asthma and hay fever, breastfeeding, number of siblings, heating system, carpets in student's bedroom, pet ownership, getting rid of carpets because of the child's allergy, students active smoking, mother filling in the questionnaire and parental perception of air pollution as a risk factor for their child's respiratory health