Reliability in reporting asthma history and age at asthma onset

Background: Evaluation of the prevalence and incidence of asthma and research into its etiology often rely on self-reported information. We conducted this analysis to investigate reliability in reporting asthma history across categories of demographic and socio-economic characteristics. Methods: We analyzed data from 3109 participants in the Coronary Artery Risk Development in Young Adults study, a longitudinal study of African-American and white adults. Responses to self-administered questionnaires completed at 15- and 20-year follow-up exams were used to evaluate agreement in reporting asthma history and age at diagnosis and assess variation in agreement across categories of demographic and health-related characteristics. Results: A history of asthma was reported by 12% of participants at the 15-year exam and 11% of participants at the 20-year exam, with 97% agreement and an overall Kappa coefficient of 0.845 (95% confidence interval: 0.815-0.874). Kappa coefficients were higher among women than men and increased monotonically across categories of educational attainment. One-hundred eight participants (35%) reported exactly the same age at diagnosis at the two time points; for another 120 (39%), the difference in reported ages was <= 2 years. Age at asthma diagnosis reported at the 20-year exam was, on an average, 1 year (SD: 5.2) older than that reported at the 15-year exam. Conclusions: Five-year reliability in self-reported asthma history is high, and variation in reporting age at diagnosis is low across categories of participant characteristics. Nevertheless, agreement in responses at two times does not guarantee that self-administered questionnaires are sensitive tools for detecting a true asthma history.