title: The HUNT study: participation is associated with survival and depends on socioeconomic status, diseases and symptoms.
abstract: BACKGROUND
  Population based studies are important for prevalence, incidence and association studies, but their external validity might be threatened by decreasing participation rates. The 50 807 participants in the third survey of the HUNT Study (HUNT3, 2006-08), represented 54% of the invited, necessitating a nonparticipation study.
  
  
  METHODS
  Questionnaire data from HUNT3 were compared with data collected from several sources: a short questionnaire to nonparticipants, anonymous data on specific diagnoses and prescribed medication extracted from randomly selected general practices, registry data from Statistics Norway on socioeconomic factors and mortality, and from the Norwegian Prescription Database on drug consumption.
  
  
  RESULTS
  Participation rates for HUNT3 depended on age, sex and type of symptoms and diseases, but only small changes were found in the overall prevalence estimates when including data from 6922 nonparticipants. Among nonparticipants, the prevalences of cardiovascular diseases, diabetes mellitus and psychiatric disorders were higher both in nonparticipant data and data extracted from general practice, compared to that reported by participants, whilst the opposite pattern was found, at least among persons younger than 80 years, for urine incontinence, musculoskeletal pain and headache. Registry data showed that the nonparticipants had lower socioeconomic status and a higher mortality than participants.
  
  
  CONCLUSIONS
  Nonparticipants had lower socioeconomic status, higher mortality and showed higher prevalences of several chronic diseases, whilst opposite patterns were found for common problems like musculoskeletal pain, urine incontinence and headache. The impact on associations should be analyzed for each diagnosis, and data making such analyses possible are provided in the present paper.
authors.affiliation: HUNT Research Centre, Department of Public Health and General Practice, Norwegian University of Science and Technology, Levanger, Norway. arnulf.langhammer@ntnu.no
authors.forename: Arnulf
authors.initials: A
authors.lastname: Langhammer
authors.forename: Steinar
authors.initials: S
authors.lastname: Krokstad
authors.forename: Pål
authors.initials: P
authors.lastname: Romundstad
authors.forename: Jon
authors.initials: J
authors.lastname: Heggland
authors.forename: Jostein
authors.initials: J
authors.lastname: Holmen
mesh_terms: D000328:Adult; D017677:Age Distribution; D000369:Aged, 80 and over; D000886:Anthropometry; D005260:Female; D006331:Heart Diseases; D006801:Humans; D008019:Life Style; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D010358:Patient Participation / Q000706:statistics & numerical data; D015995:Prevalence; D011788:Quality of Life; D017678:Sex Distribution; D012923:Social Class; D011795:Surveys and Questionnaires / Q000592:standards*; D016019:Survival Analysis