Comparison of PLACE and RDS
PLACE is a venue-based method for sampling most at risk populations. Respondent driven sampling (RDS) is a social network-based sampling strategy. Both methods ask respondents about their characteristics and behavior and both can be used to monitor indicators recommended in the Framework for Monitoring and Evaluating HIV Prevention Programs for Most-at-Risk Populations published by UNAIDS.
Although both methods can provide estimates of key HIV behavioral indicators, the methods are quite different. RDS is a network based method that selects "seeds" or initial recruits to identify additional respondents that are brought to the interviewing site. These initial respondents subsequently select additional respondents for interview who then recruit additional respondents until an adequate number of respondents is obtained. The method is reminiscent of "snowball" sampling, however, RDS provides an unbiased estimate of indicators if the method's assumptions are met. (See Heckathorn DD, Respondent-Driven Sampling: A New Approach to the Study of Hidden Populations Social Problems, Vol. 44, No. 2 (May, 1997), pp. 174-199). Assessing whether the assumptions are met can be challenging according to Dr. Giovanna Merli of the University of Wisconsin who is conducting a study to assess the extent to which RDS assumptions are being met in an RDS study in China. One of the assumptions difficult to assess is the assumption that none of the eligible people in the risk group is so socially isolated that he or she is not socially connected to the social network of interest. People who are socially isolated would be missed by RDS if there is no opportunity for them to be recruited because they have no peer contacts. Similarly, people who are known but unable or unwilling to visit the RDS interview site are also missed from the survey. The RDS approach has the advantage of not requiring the identification of venues or a strategy to sample individuals at venues.
PLACE requires the identification of venues, the construction of a sampling frame of venues, and selection of venues where individual interviews will be conducted. Venues include traditional venues such as bars and clubs as well as non-traditional venues such as parks, fast food restaurants, street corners, and taxi stands. The protocol for selecting a representative sample of venue patrons at PLACE sites is described in detail in the protocol. Individuals who do not visit traditional or non-traditional venues to socialize will be missed by the PLACE method much as individuals who do not connect to the social network will be missed by RDS.
There are other differences as well. Determination of whether a person is a sexworker, MSM or injecting drug user is partially decided by the respondent-recruiter in RDS based on information provided to him or her by the study staff. The recruiter will determine which of her social contacts is a sexworker or not and randomly select one of the sexworkers to visit the RDS interview site. If the recruiter does not know the sexworker status of some of her social contacts, the final sample may under-represent sexworkers less willing to self-identify to their peers as sexworkers. Determination of whether a person is a member of a particular risk group in the PLACE method is based on the respondent's answers to behavioral questions, e.g., have you received cash in exchange for sex in the past 12 months? This will underrepresent sexworkers who refuse to acknowledge sexwork to an interviewer.