Respondent Driven Sampling (RDS) Keith Chan BC CfE

RDS of drug users in Recife, Brazil IDU DU

Douglas Heckathorn, Cornell

Obstacles Hard to reach populations Lack of sampling frame Convenience sample Biased estimates Not generalizable

RDS hopes Valid identification of population members Population-based estimates Efficient recruitment of hidden populations

RDS issues Many assumptions and requirements Many potential biases may not disappear Difficulties in analysis of RDS data Success and failures of RDS worldwide

RDS Assumptions 1.Recruits who’s network is members of the target population 2.Network forms one single large component 3.Report network size accurately 4.Recruit randomly from network 5.Sampling with replacement

RDS Necessary Data Requirements 1.Personal Network Size 2.Respondent's Serial Number - Serial number of the coupon the respondent was recruited with 3.Respondent's Recruiting Serial Numbers - Serial numbers from the coupons the respondent is given to recruit others

Important Coupon Information

RDS of drug users in Recife, Brazil IDU Non IDU

RDS study of MSM, Kampala, Uganda

Markov Process Assumption Memoryless As the recruitment process continues from wave to wave, an equilibrium mix of recruits will eventually be attained This equilibrium mix is independent of the characteristics of the subject from which the recruitment began

Equilibrium of education, MSM, Uganda Did not complete high school Completed high school

No foreign sex partner Had any foreign sex partner Equilibrium of sex with foreigners, MSM, Uganda

Network Size Question Meant to assess the size of the network from which a person could actually recruit within a reasonable time 1.How many other ____ do you know and you will see in the next month? 2.How many other ____ do you know and you will see in the next week?

Reciprocal Relationship Assumption

Analysis Sample size calculation Crude vs. adjusted Univariate Bivariate Weights Multivariate Netdraw Aggregate analyses Statistical tests Design effect adjustment

RDS of drug users in Recife, Brazil IDU seed Never grew. Requested from Brazilia permission to change to all drug users.

RDS of drug users in Recife, Brazil IDU DU

IDU: Failures Russia Kosovo

IDU: Successes USA Indonesia India VietnamMexico Estonia Russia Thailand Nepal MontenegroSerbia Iran

Female sex workers: Failures Serbia, Montenegro, Albania, Russia Caribbean Paraguay

Female sex workers: Successes Honduras Papua New Guinea India Vietnam

MSM: Failures Kosovo Caribbean Albania Estonia Cambodia

MSM: Successes Honduras Papua New Guinea Bangladesh Zanzibar Thailand Nepal Croatia Egypt Uganda USA Iran South Africa Brazil