title: Implementation of Web-Based Respondent Driven Sampling among Men Who Have Sex with Men in Sweden.
abstract: BACKGROUND
  Respondent driven sampling (RDS) was designed to study 'hidden' populations, for which there are no available sampling frame. RDS has been shown to recruit far into social networks of the study population and achieve unbiased estimates when certain assumptions are fulfilled. Web-based respondent driven sampling (WebRDS) has been implemented among MSM in Vietnam and produced a sufficient sample of MSM. In order to see if WebRDS could work in a 'hidden' population in a high-income setting, we performed a WebRDS among MSM in Sweden to study a sensitive topic, sexual risk behaviour for HIV/STI and Internet use.
  
  
  METHODS
  A cross-sectional survey was implemented between July 11, 2012 and January 21, 2013 by using a WebRDS software. Men, fifteen years old or above, who reported having ever had sex with another man were included. The web-survey explored sociodemographics, sexual risk behaviour for HIV/STI and Internet use.
  
  
  RESULTS
  The WebRDS process created a sample of 123 eligible respondents. The mean age among participants was 32 years old. All respondents reported having had unprotected anal intercourse (UAI) with at least one regular and one casual sex partner during the last 12 months. On average participants reported having had UAI with three casual sexual partners and in total having had seven casual sex partners during the last 12 months.
  
  
  CONCLUSIONS
  The WebRDS produced a sample of Internet-using MSM in Sweden who all reported sexual risk behaviour for HIV/STI during the last 12 months. It holds promise for future online studies among MSM and a possibility to reach MSM at risk for HIV/STI with interventions or information. Some challenges were found including short recruitment chains, and further research need to address how to optimize WebRDS online recruitment methods in high income settings.
authors.affiliation: Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Susanne
authors.initials: S
authors.lastname: Strömdahl
authors.affiliation: Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden; College of Information System and Management, National University of Defense Technology, Changsha, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Lu
authors.affiliation: Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Linus
authors.initials: L
authors.lastname: Bengtsson
authors.affiliation: Department of Sociology, Stockholm University, Stockholm, Sweden.
authors.forename: Fredrik
authors.initials: F
authors.lastname: Liljeros
authors.affiliation: Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Thorson
mesh_terms: D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D015658:HIV Infections / Q000453:epidemiology; D018451:Homosexuality, Male / Q000706:statistics & numerical data*; D006801:Humans; D007182:Income; D020407:Internet / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D012309:Risk-Taking; D011795:Surveys and Questionnaires; D013548:Sweden; D055815:Young Adult