An assessment of respondent-driven sampling to recruit illicit drug users, men who have sex with men, and sex partners of both groups

Background: Hidden populations at elevated risk for HIV, such as illicit drug users and bisexual men of color, can be hard to reach and are not amenable to random sampling. Novel approaches should be developed and tested for studying such populations. Respondent-driven sampling (RDS) seeks to construct samples from populations that lack comprehensive sampling frames needed for random sampling, while reducing biases associated with chain-referral methods. RDS is based on the recognition that, if allowed to continue through enough waves, the sample attains a stable composition (equilibrium) independent of the initial choice of subjects. Methods: Respondent-driven sampling was used to recruit persons who use ‘hard' drugs, men who had sex with men, and sex partners of both groups for a study of the sexual diffusion of HIV. RDS assumes that those best able to access members of hidden populations are their own peers. RDS motivates peers by offering incentives both for being interviewed and for referring others to the study. Results: To date, six “seed” recruiters produced 1091 study participants. Most (84%) reported recent ‘hard' drug use, and 20% of sexually active men were behaviorally bisexual. While recruitment chains were long, the sample typically converged to equilibrium (new participants were independent of the “seeds” who began the recruiting chains) within four waves for most key participant characteristics. Socioeconomic diversity was problematic, however. Discussion: RDS is effective for sampling hard-to-reach populations, but attention is needed to recruit persons other than those of low socioeconomic status.