Does size really matter? A sensitivity analysis of number of seeds in a respondent-driven sampling study of gay, bisexual and other men who have sex with men in Vancouver, Canada.

Background: Respondent-driven sampling (RDS) is an increasingly used peer chain-recruitment method to sample "hard-to-reach" populations for whom there are no reliable sampling frames. Implementation success of RDS varies; one potential negative factor being the number of seeds used.

Methods: We conducted a sensitivity analysis on estimates produced using data from an RDS study of gay, bisexual and other men who have sex with men (GBMSM) aged ≥16 years living in Vancouver, Canada.