What makes a respondent-driven sampling "seed" productive? Example of finding at-risk Massachusetts men who have sex with men.

Several recent studies have sought to elaborate upon the applicability and validity of respondent-driven sampling (RDS) to find hard-to-reach samples in general and men who have sex with men (MSM) in particular. Few published studies have elucidated the characteristics associated with initial RDS participants ("seeds") who successfully recruited others into a study. A total of 74 original seeds were analyzed from four Massachusetts studies conducted between 2006 and 2008 that used RDS to reach high-risk MSM. Seeds were considered "generative" if they recruited two or more subsequent participants and "non-generative" if they recruited zero or one participant. Overall, 34% of seeds were generative. In separate multivariable logistic regression models controlling for age, race, health insurance, HIV status, and the study for which the seed was enrolled, unprotected anal sex in the past 12 months [adjusted odds ratio (AOR) = 6.68; 95% confidence interval (95% CI) = 1.27-35.12; p = 0.03], cocaine use during sex at least monthly during the past 12 months (AOR = 8.81; 95% CI = 1.68-46.27; p = 0.01), and meeting sex partners at social gatherings (AOR = 7.42; 95% CI = 1.58-34.76; p = 0.01) and public cruising areas (AOR = 4.92; 95% CI = 1.27-19.01; p = 0.02) were each significantly associated with increased odds of being a generative seed. These findings have methodological and practical implications for the recruitment of MSM via RDS. Finding ways to identify RDS seeds that are consistently generative may facilitate collecting a sample that is closer to reflecting the MSM who live in all of the communities in a given location or study sample.