Comparison of participants from respondent-driven sampling and service-based sampling studies of people who inject drugs

Abstract

Aims: Respondent-driven sampling (RDS) is increasingly being used to sample hidden populations, such as people who inject drugs (PWIDs). This study compared samples of PWID recruited from RDS and service-based sampling methods to explore whether RDS captured a less visible group of PWID that differed in their risk profile than those captured using service-based sampling.Methods: An RDS study of PWID was conducted in Sydney, Australia in 2009. RDS participants’ frequency of use of NSP and pharmacies was calculated. Population estimates were calculated for RDS participant characteristics and were compared with sample proportions from two separate studies, which recruited participants from needle and syringe programmes (NSP) and pharmacies.Findings: Only 12% of the RDS sample may not have been accessible through either an NSP or a pharmacy. RDS participants were just as risky in their injecting practices and were more likely to access HCV prevention services than participants recruited from service-based sampling methods.Conclusions: This comparison was useful in evaluating who might be missed in service-based sampling methods. Given that RDS was not able to capture a less visible group of PWID, the choice of sampling method should take into account the availability of services through which to conduct a study.