Table 1 Prevalence of selected characteristics of the study population surveyed in 1998 and in 2001.
| Variable | n* | Prevalence (%) |
|---|---|---|
| Age in 1998 survey (years)† | ||
| 1.0–1.99 | 1085 | 25 |
| 2.0–2.99 | 1099 | 25 |
| 3.0–3.99 | 1113 | 25 |
| 4.0–4.99 | 1102 | 25 |
| Boys | 2304 | 52 |
| Girls | 2095 | 48 |
| Mother has asthma | 554 (3203) | 17 |
| Coal heating in the home | ||
| 1998 | 203 (3410) | 6 |
| 2001 | 199 (2735) | 7 |
| Smoking by household member in the home | ||
| 1998 | 1144 (3382) | 34 |
| 2001 | 793 (2543) | 31 |
| Either parent continued education past 16 years of age | 1986 (3012) | 66 |
*Number of children (total of replies in each category).
†A total of 4400 children were selected for the survey in 1998.
Other covariates examined were preterm birth, breast feeding, father with asthma, gas cooking, presence of pets, number of cigarettes smoked by mother, overcrowding, single parenthood, and diet.