title: Estimating design effect and calculating sample size for respondent-driven sampling studies of injection drug users in the United States.
abstract: Respondent-driven sampling (RDS) has become increasingly popular for sampling hidden populations, including injecting drug users (IDU). However, RDS data are unique and require specialized analysis techniques, many of which remain underdeveloped. RDS sample size estimation requires knowing design effect (DE), which can only be calculated post hoc. Few studies have analyzed RDS DE using real world empirical data. We analyze estimated DE from 43 samples of IDU collected using a standardized protocol. We find the previous recommendation that sample size be at least doubled, consistent with DE = 2, underestimates true DE and recommend researchers use DE = 4 as an alternate estimate when calculating sample size. A formula for calculating sample size for RDS studies among IDU is presented. Researchers faced with limited resources may wish to accept slightly higher standard errors to keep sample size requirements low. Our results highlight dangers of ignoring sampling design in analysis.
authors.affiliation: Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. cwejnert@cdc.gov
authors.forename: Cyprian
authors.initials: C
authors.lastname: Wejnert
authors.forename: Huong
authors.initials: H
authors.lastname: Pham
authors.forename: Nevin
authors.initials: N
authors.lastname: Krishna
authors.forename: Binh
authors.initials: B
authors.lastname: Le
authors.forename: Elizabeth
authors.initials: E
authors.lastname: DiNenno
mesh_terms: D000293:Adolescent; D000328:Adult; D055030:Drug Users / Q000706:statistics & numerical data*; D015340:Epidemiologic Research Design; D005260:Female; D006679:HIV Seropositivity / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010379:Peer Group; D012017:Referral and Consultation; D012309:Risk-Taking; D018401:Sample Size; D012494:Sampling Studies; D018571:Sentinel Surveillance; D015819:Substance Abuse, Intravenous / Q000453:epidemiology*; D014481:United States / Q000453:epidemiology; D055815:Young Adult