Time-dependent variation in the responses to the web-based ISAAC questionnaire.

BACKGROUND Epidemiologic studies have shown seasonal variations in responses to the written questionnaire for rhinitis symptoms. OBJECTIVE To evaluate whether the timing of data collection affected responses to the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire in a Web-based study. METHODS The Web-based ISAAC questionnaires were completed by parents with children 6 to 12 years old using an online research system. The authors conducted surveys of asthma symptoms every month for 1 year and surveys of rhinitis and eczema symptoms every season throughout 1 entire year. RESULTS There was a significant fluctuation in the positive responses to questions about wheezing in the past 12 months (P < .001) but not in the positive responses to questions about exercise-induced wheezing in the past 12 months and asthma ever (P = .75 and P = .15, respectively). The positive responses to questions about rhinitis and allergic rhinoconjunctivitis in the past 12 months and pollinosis ever exhibited significant seasonal variations (P = .002, P < .001, and P < .001, respectively). In contrast, there were no significant variations in positive responses regarding eczema in the past 12 months and eczema ever (P = .33 and P = .55, respectively). CONCLUSION There were time-dependent fluctuations in responses to the Web-based questionnaire regarding allergic symptoms. Timing of data collection should be taken into account when evaluating prevalence of asthma and rhinitis in children.