P1-S4.33 Effectiveness of respondent driven sampling among undocumented Central American Immigrant Women in Houston, Texas, 2010

Background Respondent driven sampling (RDS) is a social research method that uses participants’ social networks (SNs) to access members of hidden populations for which there is no sampling frame. RDS is widely used for HIV behavioural research among sex workers, drug users, and other hidden populations. However, it has had minimum application in migrant populations. We used RDS to conduct an HIV behavioural survey among undocumented Central American immigrant women in Houston, Texas (specifically, Guatemalan, Honduran, and El Salvadoran females, ages 18–50 years, residing in Houston without a valid US visa or residency papers). Here we describe the effectiveness of RDS to recruit members of this population. Methods Formative research indicated that social ties are mainly formed by country of origin, age, and number of years living in the USA. Measures of effectiveness were survey duration, participants' adoption of the recruitment system, SN density, homophily, and attainment of equilibrium. SN density is the average number of social ties per participant. Homophily is the likelihood that individuals recruit individuals like themselves; scores range from −1 to 1, where 1=100% within-group recruitment and 0=100% random recruitment. Equilibrium is the stable sample composition that indicates independence from initial non-randomly selected participants. Results Beginning with three initial participants, we recruited a sample of 230 immigrant women over 16 weeks. Participants adopted the recruitment system with reasonable ease (46% recruited ≥1 peers) and SNs were dense (mean SN size=20). Homophily (H) was moderate by country of origin (Guatemalans: H=0.52; El Salvadorans: H=0.42) and low by age and number of years in the USA (H≤0.25). Equilibrium was attained for all demographic and sexual behaviour characteristics. Conclusions This study is the first to evaluate RDS in a migrant population. SNs in this population were dense, allowing recruitment to be sustained. While recruitment was moderately influenced by country of origin, women did not affiliate exclusively with those like themselves. This sociometric diversity allowed the sample to attain an equilibrium composition independent of initial participants. Overall, RDS was easy to implement, attained a large sample in a relatively short period of time, and reached an otherwise hidden population. RDS is an effective method for recruiting undocumented Central American immigrant women for HIV behavioural survey