Agreement between asthma questionnaire and health care register data.

PURPOSE: Risk factors and consequences of asthma can be studied by using validated questionnaires. The overall objective of this study was to assess the agreement of parental-reported asthma-related questions regarding their children against Swedish health care registers. METHODS: We linked a population-based twin cohort of 27 055 children aged 9 to 12 years to the Swedish Prescribed Drug Register, National Patient Register, and the primary care register. Parent-reported asthma was obtained from questionnaires, and diagnoses and medication were retrieved from the registers. For the agreement between the questionnaire and the registers, Cohen's kappa was estimated. RESULTS: The kappa of the "reported ever asthma" against a "register-based ever asthma" was 0.69 and 0.57 between the parental-"reported doctor's diagnosis" and "register-based doctor's diagnosis." The highest agreement between "reported current asthma" and "register-based current asthma" with at least 1 dispensed medication or a diagnosis applied to different time windows was seen for an 18-month window (kappa = 0.70). CONCLUSIONS: We found that parent-reported asthma-related questions showed on average good agreement with the Swedish health care registers. This implies that in-depth questionnaires with rich information on phenotypes are suitable proxies for asthma in general and can be used for health care research purposes.