Balancing Theory and Practice in Respondent-Driven Sampling: A Case Study of Innovations Developed to Overcome Recruitment Challenges

et al. (2013) Balancing Theory and Practice in Respondent-Driven Sampling: A Case Study of Innovations Developed to Overcome Recruitment Challenges. PLoS ONE 8(8): e70344. doi:10.1371/journal.pone.0070344 Balancing Theory and Practice in Respondent-Driven Sampling: A Case Study of Innovations Developed to Overcome Recruitment Challenges Hong-Ha M. Truong 0 Michael Grasso 0 Yea-Hung Chen 0 Timothy A. Kellogg 0 Tyler Robertson 0 Alberto Curotto 0 Wayne T. Steward 0 Willi McFarland 0 Javier R. Lama, Asociacion Civil Impacta Salud y Educacion, Peru 0 1 Department of Medicine, University of California San Francisco , San Francisco , California, United States of America, 2 Gladstone Institute of Virology and Immunology , San Francisco , California, United States of America, 3 Department of Public Health , San Francisco, California , United States of America Introduction: 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. - Funding: This work was supported by the National Institute of Mental Health at the National Institutes of Health (R01 MH080657 and R01 MH080657-03S1; PI: HMT). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. For research studies that entail the recruitment of a hard-toreach target population, obtaining a meaningfully large and representative sample can be difficult. A methodology from the field of sociological research known as respondent-driven sampling (RDS) offers an approach through the use of chain referrals with statistical adjustments to approximate a probability basis [13]. RDS uses long-chain referral whereby members of the target population recruit other members, similar to snowball sampling. The RDS recruitment process starts with purposeful selection of an initial set of participants, also referred to as seeds. The seeds cover the diversity of the target population with respect to factors describing social groupings, such as demographic characteristics and behaviors of interest. Ideally, they have large social networks from which to recruit other eligible participants. Peer-recruited participants who enroll in the study or enrolled referrals would in turn refer additional participants. These successive recruitment cycles or waves continue until sample stability and targeted sample size are reached. A sample that reaches equilibrium provides a basis for adjusting estimates to be representative of the entire target population. Relative network sizes are used to estimate differential recruitment probabilities. Recruitment linkages between participants are used to estimate design effects and their impact on standard errors. The ultimate goal of obtaining a sufficiently large and representative sample is achievable if the RDS study adheres to several underlying theoretical assumptions, including respondents report the size of their social network accurately, respondents recruit randomly from their social network and network connections are reciprocal [4]. Efficiency of accrual and guarantee of participant eligibility with peer-referral strategies are based on the rationale that individuals who are members of the social network will have better access to the target population than outsiders, e.g., study staff. Validity of the sample is based on correcting for different probabilities of inclusion by network size and adjusting for similarities between the recruiter and recruits. RDS has been used in public health research studies around the world. A systematic review of global RDS studies concluded this methodology can be successfully implemented to recruit populations at high risk for HIV for behavioral and biological surveys [5]. In the field of HIV research, the target population is often high-risk groups such as injection drug users, female sex workers and men who have sex with men (MSM) [68]. However, RDS faces logistical and theoretical challenges that could threaten efficiency and validity in settings worldwide. In our study, International Travel Research to Inform Prevention or I-TRIP, we encountered barriers to using conventional RDS methodology. We found our target population of MSM who travel internationally presented an unusual challenge in the recruitment of a representative sample. The challenges revolved around two key components of conventional RDS: use of paper coupons for recruitment and the secondary incentives structure. In a conventional RDS study, participants are asked to recruit others from their social network upon completion of the survey. Those willing to recruit are provided with coded, non-replicable paper coupons to give to potential participants. The coupons are designed to help track and verify the recruiter-recruit relationship for the purposes of data analysis and secondary incentives. However, the need to meet face-to-face to give the cou (...truncated)