title: Implementation of web-based respondent-driven sampling among men who have sex with men in Vietnam.
abstract: OBJECTIVE
  Lack of representative data about hidden groups, like men who have sex with men (MSM), hinders an evidence-based response to the HIV epidemics. Respondent-driven sampling (RDS) was developed to overcome sampling challenges in studies of populations like MSM for which sampling frames are absent. Internet-based RDS (webRDS) can potentially circumvent limitations of the original RDS method. We aimed to implement and evaluate webRDS among a hidden population.
  
  
  METHODS
  This cross-sectional study took place 18 February to 12 April, 2011 among MSM in Vietnam. Inclusion criteria were men, aged 18 and above, who had ever had sex with another man and were living in Vietnam. Participants were invited by an MSM friend, logged in, and answered a survey. Participants could recruit up to four MSM friends. We evaluated the system by its success in generating sustained recruitment and the degree to which the sample compositions stabilized with increasing sample size.
  
  
  RESULTS
  Twenty starting participants generated 676 participants over 24 recruitment waves. Analyses did not show evidence of bias due to ineligible participation. Estimated mean age was 22 years and 82% came from the two large metropolitan areas. 32 out of 63 provinces were represented. The median number of sexual partners during the last six months was two. The sample composition stabilized well for 16 out of 17 variables.
  
  
  CONCLUSIONS
  Results indicate that webRDS could be implemented at a low cost among Internet-using MSM in Vietnam. WebRDS may be a promising method for sampling of Internet-using MSM and other hidden groups.
authors.affiliation: Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden. bengtssonlinus@gmail.com
authors.forename: Linus
authors.initials: L
authors.lastname: Bengtsson
authors.forename: Xin
authors.initials: X
authors.lastname: Lu
authors.forename: Quoc Cuong
authors.initials: QC
authors.lastname: Nguyen
authors.forename: Martin
authors.initials: M
authors.lastname: Camitz
authors.forename: Nguyen Le
authors.initials: NL
authors.lastname: Hoang
authors.forename: Tuan Anh
authors.initials: TA
authors.lastname: Nguyen
authors.forename: Fredrik
authors.initials: F
authors.lastname: Liljeros
authors.forename: Anna
authors.initials: A
authors.lastname: Thorson
mesh_terms: D000328:Adult; D006284:Health Plan Implementation; D006306:Health Surveys / Q000706:statistics & numerical data*; D018451:Homosexuality, Male / Q000706:statistics & numerical data*; D006801:Humans; D020407:Internet; D008297:Male; D011157:Population Dynamics; D018401:Sample Size; D013997:Time Factors; D014744:Vietnam / Q000453:epidemiology