Validity of parental-reported questionnaire data on Danish children's use of asthma-drugs: a comparison with a population-based prescription database.

The aim of this study was to examine the validity--estimated as the sensitivity, specificity, and predictive values--of questionnaire-based parental reporting on Danish children's use of asthma drugs. Within a population-based cross-sectional study on the association between asthma and dental anxiety, we compared parental answers on their children's use of asthma drugs during the past 12 months with National Health Service (NHS) data from a prescription database on prescriptions of inhaled beta 2-agonists, inhaled corticosteroids, or both for a period of 14 months preceding the date of posting the parental questionnaires. In four municipalities in North Jutland County, Denmark, in 2001, parents of 1273 children between the ages of 6 and 8 years completed the questionnaire. For frequency of use, the sensitivity increased from 57.9% (95% confidence interval [CI]: 47.8-67.3%) for the answer 'Every day' to 91.6% (95% CI: 84.3-95.7%) when the answers 'Every day', 'Often', and 'Sometimes' were combined. The specificity exceeded 95.9% (95% CI: 94.6-96.9%) for all answers. The positive predictive value (PPV) increased from 64.4% (95% CI: 56.1-72.0%) when the answers 'Every day', 'Often', and 'Sometimes' were combined to 94.8% (95% CI: 85.9-98.2%) for the answer 'Every day'. The negative predictive value (NPV) both exceeded 96.7% (95% CI: 95.5-97.6%) for all answers. Questionnaire-based parental reporting on children's one-year asthma-drug use appears to be valid in epidemiological research depending on the study question and design.