| This study determined the sensitivity and specificity of questionnaires and administrative databases compared to a clinical reference standard for asthma.;208 schoolchildren from a population-based sample participated. They underwent a physician assessment, spirometry, methacholine challenge, exhaled nitric oxide and skin testing. Data was linked to the Ontario Asthma Surveillance Information System.;"Questionnaire diagnosis" was an affirmative response to physician-diagnosed asthma. "Database diagnosis" was 2 outpatient visits or 1 hospitalization within 2 years. "Clinical diagnosis" required a physician assessment and objective findings of asthma.;"Questionnaire diagnosis" of asthma was specific (92.1%) but not sensitive (75.3%) compared to the "clinical diagnosis". "Database diagnosis" was sensitive (87.5%) but not specific (64.8%). Both sources had an excellent negative predictive value (97-98%) but poor positive predictive value (24-55%).;Epidemiologic methods accurately identify those without asthma but are poor at identifying those with asthma, leading to an overestimation of asthma prevalence and dilution of risk estimates. |
