1. Respondent Driven Sampling (RDS) Part 2 Keith Chan BC CfE

2. www.respondentdrivensampling.org www.respondentdrivensampling.org Douglas Heckathorn, Cornell

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

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

5. 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

6. 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

7. RDS of drug users in Recife, Brazil IDU DU

8. 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

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

10. 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?

11. Momentum Men's Health Study sexual health study of gay, bisexual and other men who have sex with men in Greater Vancouver. aims to report new estimates of HIV prevalence among men who have sex with men (MSM) in the region.

12. Momentum Men's Health Study Network Size Question How many gay, bisexual and other men who have sex with men aged 16 years and older do you know who live in or around the Vancouver region? –How many of these guys have you seen or spoken to in the past month? “Of these guys that you have seen or spoken to in the past month, how many do you know comfortably enough to give them a study voucher to invite their participation in the Momentum?”

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

18. Some Results

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

21. Example HIV prevalence by age group

24. In SAS proc surveyfreq data=use; table AGE_CAT*hiv_pos/cl; weight hiv_age_wt; run;

26. In SAS proc surveyfreq data=use; by AGE_CAT; table hiv_pos/cl; weight hiv_age_wt; run;

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