TY - JOUR T1 - Incidence of asthma and wheeze during adolescence – The impact of study design JF - European Respiratory Journal JO - Eur Respir J VL - 38 IS - Suppl 55 SP - p4166 AU - Linnea Hedman AU - Anders Bjerg AU - Sigrid Sundberg AU - Eva Rönmark Y1 - 2011/09/01 UR - http://erj.ersjournals.com/content/38/Suppl_55/p4166.abstract N2 - Aim: To study the impact of study design on the incidence rates of asthma and wheeze during the teen ages.Method: In a longitudinal study about asthma and allergic diseases within the OLIN studies in northern Sweden, a cohort of school children (n=3,430) was followed annually from age 7-8yrs by completion of an extended ISAAC questionnaire. In the endpoint survey (age 19yrs) 2,861 (83% of original responders) participated. Incident cases of asthma and wheeze from age 12 to 19yrs were identified by two methods: the annual questionnaire surveys and the endpoint survey only, respectively.Results: The incidence was consistently higher when the incidence was based on annual surveys compared to the endpoint survey only. Based on the endpoint survey, the average annual incidence of current asthma, physician-diagnosed asthma and ever asthma was 0.7-1.4/100/y and current wheeze was 1.5/100/y. Based on the annual surveys, the incidence of asthma was 0.9-2.7/100/y and current wheeze 3.6-5.3/100/y. In both study designs, the incidence of asthma and wheeze was higher among girls than boys (p-values<0.01). At the onset, the additional cases of current asthma identified by the annual surveys had slightly less severe asthma than those identified only in the endpoint survey (p<0.06).Conclusion: The incidence of asthma and wheeze was affected by study design. The incidence was underestimated when only baseline and endpoint data was used. Study design and follow-up time is important to consider for comparisons of the incidence of asthma and wheeze between studies. ER -