title: Balancing theory and practice in respondent-driven sampling: a case study of innovations developed to overcome recruitment challenges.
abstract: BACKGROUND
  Respondent-driven sampling (RDS) offers a recruitment strategy for hard-to-reach populations. However, RDS faces logistical and theoretical challenges that threaten efficiency and validity in settings worldwide. We present innovative adaptations to conventional RDS to overcome barriers encountered in recruiting a large, representative sample of men who have sex with men (MSM) who travel internationally.
  
  
  METHODS
  Novel methodological adaptations for the "International Travel Research to Inform Prevention" or "I-TRIP" study were offering participants a choice between electronic and paper coupons referrals for recruitment and modifying the secondary incentives structure from small cash amounts to raffle entries for periodic large cash prize raffle drawings. Staged referral limit increases from 3 to 10 referrals and progressive addition of 70 seeds were also implemented.
  
  
  RESULTS
  There were 501 participants enrolled in up to 13 waves of growth. Among participants with a choice of referral methods, 81% selected electronic referrals. Of participants who were recruited electronically, 90% chose to remain with electronic referrals when it was their turn to recruit. The mean number of enrolled referrals was 0.91 for electronic referrals compared to 0.56 for paper coupons. Median referral lag time, i.e., the time interval between when recruiters were given their referrals and when a referred individual enrolled in the study, was 20 days (IQR 10-40) for electronic referrals, 20 days (IQR 8-58) for paper coupons, 20 days (IQR 10-41) for raffle entries and 33 days (IQR 16-148) for small cash incentives.
  
  
  CONCLUSIONS
  The recruitment of MSM who travel internationally required maximizing known flexible tools of RDS while at the same time necessitating innovations to increase recruitment efficiency. Electronic referrals emerged as a major advantage in recruiting this hard-to-reach population who are of high socio-economic status, geographically diffuse and highly mobile. These enhancements may improve the performance of RDS in target populations with similar characteristics.
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, California, United States of America ; Gladstone Institute of Virology and Immunology, San Francisco, California, United States of America.
authors.forename: Hong-Ha M
authors.initials: HM
authors.lastname: Truong
authors.forename: Michael
authors.initials: M
authors.lastname: Grasso
authors.forename: Yea-Hung
authors.initials: YH
authors.lastname: Chen
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Kellogg
authors.forename: Tyler
authors.initials: T
authors.lastname: Robertson
authors.forename: Alberto
authors.initials: A
authors.lastname: Curotto
authors.forename: Wayne T
authors.initials: WT
authors.lastname: Steward
authors.forename: Willi
authors.initials: W
authors.lastname: McFarland
mesh_terms: D000293:Adolescent; D000328:Adult; D015658:HIV Infections / Q000517:prevention & control*; D018451:Homosexuality, Male; D006801:Humans; D038622:Internationality; D020407:Internet; D008297:Male; D008875:Middle Aged; D009042:Motivation; D010353:Patient Education as Topic / Q000379:methods*; D018579:Patient Selection; D012107:Research Design; D012494:Sampling Studies; D012944:Social Support; D014195:Travel; D055815:Young Adult