Evaluating respondent-driven sampling in a major metropolitan area: Comparing injection drug users in the 2005 Seattle area national HIV behavioral surveillance system survey with participants in the RAVEN and Kiwi studies.

Purpose: To empirically evaluate respondent-driven sampling (RDS) recruitment methods, which have been proposed as an advantageous means of surveying hidden populations.

Methods: The National HIV Behavioral Surveillance system used RDS to recruit 370 injection drug users (IDU) in the Seattle area in 2005 (NHBS-IDU1). We compared the NHBS-IDU1 estimates of participants' area of residence, age, race, sex, and drug most frequently injected to corresponding data from two previous surveys, the RAVEN and Kiwi Studies, and to persons newly diagnosed with HIV/AIDS and reported from 2001 through 2005.

Results: The NHBS-IDU1 population was estimated to be more likely to reside in downtown Seattle (52%) than participants in the other data sources (22%-25%), be older than 50 years of age (29% vs. 5%-10%), and report multiple races (12% vs. 3%-5%). The NHBS-IDU1 population resembled persons using the downtown needle exchange in age and race distribution. An examination of cross-group recruitment frequencies in NHBS-IDU1 suggested barriers to recruitment across different areas of residence, races, and drugs most frequently injected.

Conclusions: The substantial differences in age and area of residence between NHBS-IDU1 and the other data sources suggest that RDS may not have accessed the full universe of Seattle area injection networks. Further empirical data are needed to guide the evaluation of RDS-generated samples.