Self-reported asthma was biased in relation to disease severity while reported year of asthma onset was accurate

The aims of the study were to assess the accuracy of self-reported asthma and notified year of asthma onset. The study was performed on a sample of 365 subjects, 18–60 years old, with clinically diagnosed onset of asthma between 1983 and 1986. All subjects were investigated 10 years later, in 1996, with a respiratory questionnaire about the items of asthma and year of onset. The material was analyzed with logistic regression models. Of the 289 subjects who returned the questionnaire, asthma was reconfirmed in 251 subjects. In a logistic regression model, asthma severity was significantly associated with confirmation of asthma. The median difference between the “true” year of onset and the reported year 10 years later, the recall period was zero, with a 10th to 90th interpercentile range of –2 to 6 years. The recall period was not associated with asthma severity, bronchial hyperresponsiveness, smoking, atopy, or sex. Self-reported asthma is biased in relation to disease severity, meaning that subjects with mild disease were less prone to report their asthma. Reported year of asthma onset among adults seems to be rather accurate, with no obvious dependent misclassifications.