title: 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 how asthma 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) on asthma prevalence (3) conducted in the general population and (4) containing an explicit definition of asthma. The search was limited to the 100 most-cited papers or published since January 2010. For each paper, we recorded the asthma definition used and other variables. Then we applied the definitions to the data of the Portuguese National Asthma 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 current asthma were defined in 8, 12 and 29 different ways, respectively. By applying definitions of current asthma on INAsma 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 leading to 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.
authors.affiliation: Center for research in health technologies and information systems.- CINTESIS, Universidade do Porto, Porto, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Sá-Sousa
authors.affiliation: Center for research in health technologies and information systems.- CINTESIS, Universidade do Porto, Porto, Portugal ; Allergy Unit, Instituto CUF Porto e Hospital CUF Porto, Porto, Portugal.
authors.forename: Tiago
authors.initials: T
authors.lastname: Jacinto
authors.affiliation: Center for research in health technologies and information systems.- CINTESIS, Universidade do Porto, Porto, Portugal ; Health Information and Decision Sciences Department - CIDES, Faculdade de Medicina, Universidade do Porto, Porto, Portugal.
authors.forename: Luís Filipe
authors.initials: LF
authors.lastname: Azevedo
authors.affiliation: Allergy and Clinical Immunology Department, Hospital CUF-Descobertas, Lisboa, Portugal.
authors.forename: Mário
authors.initials: M
authors.lastname: Morais-Almeida
authors.affiliation: Allergy and Clinical Immunology Department, Hospitais da Universidade de Coimbra, Coimbra, Portugal.
authors.forename: Carlos
authors.initials: C
authors.lastname: Robalo-Cordeiro
authors.affiliation: Clínica Universitária de Pneumologia-Faculdade de Medicina de Lisboa, Lisboa, Portugal.
authors.forename: António
authors.initials: A
authors.lastname: Bugalho-Almeida
authors.affiliation: Hôpital Arnaud de Villeneuve, Centre Hospitalier Universitaire Montpellier, Montpellier, France ; Centre de recherche en Epidémiologie et Santé des Populations, CESP Inserm U1018, Villejuif, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Bousquet
authors.affiliation: Center for research in health technologies and information systems.- CINTESIS, Universidade do Porto, Porto, Portugal ; Allergy Unit, Instituto CUF Porto e Hospital CUF Porto, Porto, Portugal ; Health Information and Decision Sciences Department - CIDES, Faculdade de Medicina, Universidade do Porto, Porto, Portugal ; Faculdade de Medicina da Universidade do Porto, Rua Dr. Plácido da Costa, s/n, 4200-450 Porto, Portugal.
authors.forename: João Almeida
authors.initials: JA
authors.lastname: Fonseca
keywords: Asthma; Definition; Epidemiology; Prevalence; Review