title: Self-reported asthma was biased in relation to disease severity while reported year of asthma onset was accurate.
abstract: OBJECTIVE
  The aims of the study were to assess the accuracy of self-reported asthma and notified year of asthma onset.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Respiratory Medicine and Allergology, Sahlgrenska University Hospital, St Sigfridsgatan 85B, S-412 66, Göteborg, Sweden. Kjell.Toren@amm.gu.se
authors.forename: Kjell
authors.initials: K
authors.lastname: Torén
authors.forename: Mona
authors.initials: M
authors.lastname: Palmqvist
authors.forename: Olle
authors.initials: O
authors.lastname: Löwhagen
authors.forename: Barbro
authors.initials: B
authors.lastname: Balder
authors.forename: Alf
authors.initials: A
authors.lastname: Tunsäter
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D001249:Asthma / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D015982:Bias; D016535:Bronchial Hyperreactivity / Q000503:physiopathology; D030881:Disclosure; D005260:Female; D006801:Humans; D015994:Incidence; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012720:Severity of Illness Index; D012907:Smoking / Q000009:adverse effects; D011795:Surveys and Questionnaires