Guidelines on surveillance among populations most at risk for HIV

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LimitationsSnowball sampling has many limitations. If the goal is repeated surveillance on the same group, snowball sampling will not be appropriate. Therecan be no way to compare the results over time. Bias can result since most people tend to name acquaintances who are similar to themselvesdemographically: by race, ethnicity, education, income or religion.2.3.5 Respondent-driven samplingDescriptionRespondent-driven sampling is a modification of snowball sampling which uses a mathematical model toweight the sample data to compensate for the fact that the sample is not a simple random sample (40,41).Respondent-driven sampling is an important method for sampling hard-to-reach groups, including whenthe groups may be small relative to the general population or when a list (sampling frame) of populationmembers does not exist.To conduct respondent-driven sampling: Identify and recruit seeds (initial survey respondents). The number of seeds required varies by the totalsample size required and the diversity of the target population. Give each seed coupons and ask them to recruit three to five acquaintances. Each recruit who visits the study site brings a coupon that identifies (by number) who referred them. No names are provided, just study identification numbers combined to develop a list of the numbers ofacquaintances per study participant. Give each recruit coupons and ask them to recruit three to five acquaintances. Recruiting may go on for several waves. A mathematical model based on the Markov chain theory and network theory weights the sample toaddress the probability that people will refer their friends, making the sample less random.AdvantagesThe resulting statistical theory controls for the biases associated with chain-referral methods, providingboth population estimates and estimates of variability for those estimates (42).Individuals are accessed through their social networks, making it more likely to reach those who shun largepublic venues and avoid the street.LimitationsAs a method, respondent-driven sampling is costly and time-consuming. Sources of significant bias canexist if the population is not well networked. Entire sections of the population of interest can be missed ifthey are not connected to the initial seeds.Depending on the number of initial seeds, the start-up of a respondent-driven sampling study can be slow.Respondent-driven sampling requires specific software for analysis (available at: http://www.respondentdrivensampling.org/main.htm). Recent research has found that there is large variation in theestimates produced through respondent-driven sampling. Large sample sizes should improve on theestimates (43).There have been mixed results using respondent-driven sampling with different most-at-risk populations.In some contexts, the populations were not well networked, making respondent-driven sampling a difficultsampling strategy.A more detailed description of how to conduct respondent-driven sampling is available at: http://www.respondentdrivensampling.org/.18
Figure 2.2. Respondent-driven sampling recruitment network for one seed by type of female sex workerin Viet Nam<strong>Guidelines</strong> on surveillance among populations most at risk for HIVSource: Johnston LG et al. Effectiveness of respondent-driven sampling to recruit female sex workers in two cities in Vietnam. Journal of Urban Health, 2006, 83 (Suppl 7):16–28.http://www.springerlink.com/content/j31w862u2v65538nRespondent-driven sampling in Beijing, ChinaRespondent-driven sampling was used for three rounds of surveys to recruit men who have sex withmen in Beijing, China in 2004, 2005 and 2006. The surveys included a structured interview to collectbehavioural data and blood specimens to test for HIV, syphilis, hepatitis B virus and hepatitis C virus.The number of participants in the surveys was 325, 427 and 540 in the 2004, 2005 and 2006 surveys,respectively. In the 2004 survey, only one seed was recruited; in the 2005 and 2006 surveys, 10 and 8seeds were recruited, respectively.Special software (RDSAT) was used to adjust for the chain referral recruitment process used to selectthe sample for the survey. The software allowed researchers to make adjustments to reflect the makeupof the target population based on information from the networks of the respondents.Once adjusted, the results were representative of the population, allowing the researchers to comparethe results over time. The researchers found a rise in HIV prevalence among men who have sex withmen in Beijing over the three years and recommended urgent services for this population to slow thespread of HIV. This study was one of the first to use respondent-driven sampling for basic surveillance– comparing prevalence trends. (41)19
Page 1 and 2: UNAIDS/WHO Working Groupon Global H
Page 3 and 4: UNAIDS/WHO Working Groupon Global H
Page 5 and 6: ContentsAcknowledgements1 Introduct
Page 7 and 8: 1. IntroductionThe overall goal of
Page 9 and 10: Generalized The epidemic has mature
Page 12 and 13: Table 2.1. Potential stakeholders t
Page 14 and 15: Decide on a clear and specific defi
Page 16 and 17: In indirect sharing, one syringe is
Page 19 and 20: Sampling of subgroups of interest m
Page 21: 2.3.3 Cluster or targeted samplingD
Page 25 and 26: Time-location sampling in Harare, Z
Page 27 and 28: Surveillance among men who have sex
Page 29 and 30: 3. Conduct surveillance of populati
Page 31 and 32: When constructing a questionnaire,
Page 33 and 34: 3.2.5 Maintain confidentiality and
Page 35 and 36: HIV incidence (recent infection) is
Page 37 and 38: 4.1.4 Use the results to improve pr
Page 39 and 40: Appendix A: List of additionalsurve
Page 41 and 42: Humanimmunodeficiencyvirus (HIV)HIV
Page 43 and 44: Appendix C: LinksUNAIDS/WHO Working
Page 45 and 46: 18 Topp L et al. Representativeness
Page 47 and 48: 59 Brookmeyer R, Stroup DF (eds). M
Page 49: For more information, contact:World

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