Background: Epidemiologic data on asthma and allergies among adults are mainly based on questionnaires: this study validates the questions on asthma, allergic rhinitis, and conjunctivitis of a new Finnish questionnaire.
Methods: To validate questions used in a country-wide study among university students aged 18-25 years, we examined 150 subjects who had ever reported asthma or wheezing, and 140 without asthma symptoms. Questions were validated in relation to current diseases including 1) symptoms detected during the preceding year at the physician's interview 2) objective measurements, such as methacholine challenge, skin prick tests, and specific IgE. Data were adjusted for original proportions of "asthmatics" and"nonasthmatics" in the questionnaire study.
Results: Questions on "reported asthma" and "doctor-diagnosed asthma" had good positive predictive value (PPV) and specificity in diagnosing current asthma. The question on "attacks of shortness of breath with wheezing", and especially the question on "cough with wheezing" were most sensitive. Questions on "allergic nasal symptoms" and "allergic eye symptoms" that were "related to pollen or animals" were sensitive, but a further question on doctor's diagnosis yielded higher specificity and PPV.
Conclusion: Diagnosis-based questions were found suitable for risk-factor studies, because of their good specificity and PPV, and symptom-based questions for screening, because they were highest in sensitivity.