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.

Study design and setting: 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).

Conclusion: 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.