title: Web-based survey attracted age-biased sample with more severe illness than paper-based survey.
abstract: OBJECTIVE
  To assess how web-based recruitment is comparable to postal surveys.
  
  
  METHODS
  In 2002, we invited female users of major Norwegian websites to join a women's health study on the Internet. The results of this study on the prevalence of urinary incontinence (UI) were compared with similar data collected by post in a previous epidemiological study, EPINCONT (Epidemiology of Urinary Incontinence in Nord-Trøndelag).
  
  
  RESULTS
  Altogether 1,812 web respondents compared with 27,936 postal respondents from the EPINCONT study. The Internet sample was younger than the EPINCONT sample (37 vs. 48 years, P<0.05). The proportion of women 60 years or older was 3.3% in our study and 29.0% in the EPINCONT study. Unadjusted prevalence of UI was lower in our study (20%) than in the EPINCONT study (25%), but stratified prevalence rates were higher in all individual age groups. In the Internet sample, we found less slight UI in all age groups, and more moderate (30-39 and 50-59-year age groups) and severe UI (30-39, 40-49, and 50-59-year age groups).
  
  
  CONCLUSIONS
  We attracted a younger population with more severe UI than the EPINCONT study. Web-based approaches are less appropriate for studies on conditions concerning the older population than postal methods.
authors.affiliation: Section for General Practice, Department of Public Health and Primary Health Care, University of Bergen, Kalfarveien, Bergen, Norway. atle.klovning@medisin.uio.no
authors.forename: Atle
authors.initials: A
authors.lastname: Klovning
authors.forename: Hogne
authors.initials: H
authors.lastname: Sandvik
authors.forename: Steinar
authors.initials: S
authors.lastname: Hunskaar
mesh_terms: D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D000368:Aged; D015982:Bias; D005260:Female; D006306:Health Surveys; D006801:Humans; D020407:Internet; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D018579:Patient Selection; D015995:Prevalence; D012720:Severity of Illness Index; D014549:Urinary Incontinence / Q000453:epidemiology; D055815:Young Adult