Men who have sex with men (MSM) continue to demonstrate higher odds for HIV infection compared to the general population. Since 1994, most of the data have been derived from a chain-referral method called respondent-driven sampling (RDS). RDS relies on an invitation method to social networks that produces long recruitment chains. Although considered an effective sampling methodology, the authors question the validity of some RDS study outcomes in the MSM population because they severely underestimate risky behavior. The authors hypothesize that due to stigma and fear among casual sexual partners of being associated with HIV, the chances of MSM being invited to a study about HIV depend largely on whether they are close friends rather than past, current, or potential casual sexual and dating partners of the MSM offering the invitation. One Brazilian study of 626 participants found 11 percent of MSM reported being recruited by a “boyfriend or spouse” but only 2 percent recruited by an “occasional sexual partner.” This phenomenon may have several implications. For example, studies related to male sex workers may severely underestimate men selling sex because they may rarely receive an invitation from their regular clients. The authors recommend that future RDS studies examine composition of MSM networks (number and types of contacts), as well as participants’ reports on recruiters, to evaluate whether a rephrasing of the social network question is warranted to reflect actual inclusion probabilities.
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