title: Questionnaire layout and wording influence prevalence and risk estimates of respiratory symptoms in a population cohort.
abstract: OBJECTIVE
  Results of epidemiological studies are greatly influenced by the chosen methodology. The study aims to investigate how two frequently used questionnaires (Qs), with partly different layout, influence the prevalence of respiratory symptoms.
  
  
  METHODS
  A booklet containing two Qs, the Global Allergy and Asthma European Network Q and the Obstructive Lung Disease in Northern Sweden Q, was mailed to 30,000 subjects aged 16-75years in West Sweden; 62% responded. Sixteen questions were included in the analysis: seven identical between the Qs, four different in set-up and five with the same layout but different wording. Comparisons were made using differences in proportions, observed agreement and Kappa statistics.
  
  
  RESULTS
  Identical questions yielded similar prevalences with high observed agreement and kappa values. Questions with different set-up or differences in wording resulted in significantly different prevalences with lower observed agreement and kappa values. In general, the use of follow-up questions, excluding subjects answering no to the initial question, resulted in 2.9-6.7% units lower prevalence.
  
  
  CONCLUSIONS
  The question set-up has great influences on epidemiological results, and specifically questions that are set up to be excluded based on a previous no answer leads to lower prevalence compared with detached questions. Therefore, Q layout and exact wording of questions has to be carefully considered when comparing studies.
authors.affiliation: Department of Internal Medicine, Krefting Research Centre, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. linda.ekerljung@gu.se
authors.forename: Linda
authors.initials: L
authors.lastname: Ekerljung
authors.forename: Eva
authors.initials: E
authors.lastname: Rönmark
authors.forename: Jan
authors.initials: J
authors.lastname: Lötvall
authors.forename: Göran
authors.initials: G
authors.lastname: Wennergren
authors.forename: Kjell
authors.initials: K
authors.lastname: Torén
authors.forename: Bo
authors.initials: B
authors.lastname: Lundbäck
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001249:Asthma / Q000453:epidemiology*; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D015995:Prevalence; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D012720:Severity of Illness Index; D017678:Sex Distribution; D011795:Surveys and Questionnaires / Q000592:standards*; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult