Class lists from the seven randomly selected schools identified 309 children in grade 4. Four children were excluded because their parents could not understand the study sufficiently to give informed consent, and a further six parents refused consent for any part of the study. Nine children had moved from the selected school before the study took place, leaving 290 children for whom the parent provided adequate questionnaire information (68 by telephone interview). Of these, 268 children were interviewed at school and 229 undertook methacholine challenge; 22 did not provide parental consent for interview, one child was not challenged because of significant baseline airflow obstruction, and 38 did not provide parental or personal consent for methacholine challenge. Of the 290 children with completed parent questionnaires, 150 (51.7%) were male, and the majority (80%) were aged nine years (range 8.6 to 10.7 years). Best quality drugs are available at the best pharmacy that you can start shopping with right now whenever you need buy birth control, never having to doubt the choice made or the quality of the drug you get.

Slightly more than half of the 229 children whose parents permitted their full participation were male (55.0%), but the group had the same age distribution, ethnic background, range of socioeconomic class as judged by parental occupation, and family history of atopy and asthma; the slightly greater prevalences of respiratory symptoms in the 229 children fully assessed compared with the whole sample of 290 were not statistically significant (Table 1).

TABLE 1
Comparison of all 290 children with parent-completed questionnaires with 229 children completing all assessments including methacholine challenge test and child questionnaire

Sample with parental questionnaire Sample fully assessed
Number 290 229
Characteristics of the children
Male 150 (51.7%) 126 (55.0%)
Age (years)
8 16 (5.5%) 13 (5.7%)
9 232 (80.0%) 185 (80.8%)
10 42 (14.5%) 31 (13.5%)
European parents 271 (93.4%) 213 (93.0%)
Canadian-born 263 (90.7%) 207 (90.4%)
Family history of atopy 147 (50.7%) 116 (50.7%)
Family history of asthma 33 (11.4%) 26 (11.4%)
Child symptoms reported by the parent
Diagnosed asthma 26 (9.0%) 21 (9.2%)
Wheezing 74 (25.5%) 61 (26.6%)
Recurrent cough only 32 (11.0%) 27 (11.8%)
Hayfever 106 (36.6%) 88 (38.4%)

Differences between the groups are all nonsignificant