Operational definitions of asthma in recent epidemiological studies are inconsistent.

Abstract : Objective:The best combination of questions to define asthma in epidemiological asthma studies is not known.We summarized the operational definitions of asthma used in prevalence studies and empirically assess howasthma prevalence estimates vary depending on the definition used.Methods:We searched the Thomson Reuters ISI Web of knowledge and included (1) cross-sectional studies (2) onasthma prevalence (3) conducted in the general population and (4) containing an explicit definition of asthma. Thesearch was limited to the 100 most-cited papers or published since January 2010. For each paper, we recorded theasthma definition used and other variables. Then we applied the definitions to the data of the Portuguese NationalAsthma survey (INAsma) and of the 2005–2006 National Health and Nutrition Examination Survey (NHANES)computing asthma prevalence estimates for the different definitions.Results:Of 1738 papers retrieved, 117 were included for analysis. Lifetime asthma, diagnosed asthma and currentasthma were defined in 8, 12 and 29 different ways, respectively. By applying definitions of current asthma onINAsma and NHANES data, the prevalence ranged between 5.3%-24.4% and 1.1%-17.2%, respectively.Conclusions:There is considerable heterogeneity in the definitions of asthma used in epidemiological studies leadingto highly variable estimates of asthma prevalence. Studies to inform a standardized operational definition are needed.Meanwhile, we propose a set of questions to be reported when defining asthma in epidemiological studies.