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Respondent Driven Sampling (RDS). Keith Chan BC CfE. RDS of drug users in Recife, Brazil. IDU. DU. www.respondentdrivensampling.org Douglas Heckathorn, Cornell. Obstacles. Hard to reach populations Lack of sampling frame Convenience sample Biased estimates Not generalizable. RDS hopes.
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Respondent Driven Sampling (RDS) Keith Chan BC CfE
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 • Recruits who’s network is members of the target population • Network forms one single large component • Report network size accurately • Recruit randomly from network • Sampling with replacement
RDS Necessary Data Requirements • Personal Network Size • Respondent's Serial Number - Serial number of the coupon the respondent was recruited with • Respondent's Recruiting Serial Numbers - Serial numbers from the coupons the respondent is given to recruit others
RDS of drug users in Recife, Brazil IDU Non IDU
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 Completed high school Did not complete high school
Equilibrium of sex with foreigners, MSM, Uganda No foreign sex partner Had any foreign sex partner
Network Size Question Meant to assess the size of the network from which a person could actually recruit within a reasonable time How many other ____ do you know and you will see in the next month? How many other ____ do you know and you will see in the next week?
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.
Kosovo Russia IDU: Failures
Mexico Vietnam USA Estonia Nepal Iran Russia Thailand Montenegro Serbia India Indonesia IDU: Successes
Caribbean Paraguay Serbia, Montenegro, Albania, Russia Female sex workers: Failures
Honduras Vietnam India Papua New Guinea Female sex workers: Successes
Estonia Caribbean Cambodia Albania Kosovo MSM: Failures
USA Honduras Egypt Croatia Nepal Iran Brazil Uganda Thailand Zanzibar Papua New Guinea Bangladesh South Africa MSM: Successes