Using Partially-Observed Facebook Networks to Develop a Peer-Based HIV Prevention Intervention: Case Study.

BACKGROUND: This is a case study from an HIV prevention project among young black men who have sex with men. Individual-level prevention interventions have had limited success among young black men who have sex with men, a population that is disproportionately affected by HIV; peer network-based interventions are a promising alternative. Facebook is an attractive digital platform because it enables broad characterization of social networks. There are, however, several challenges in using Facebook data for peer interventions, including the large size of Facebook networks, difficulty in assessing appropriate methods to identify candidate peer change agents, boundary specification issues, and partial observation of social network data. OBJECTIVE: This study aimed to explore methodological challenges in using social Facebook networks to design peer network-based interventions for HIV prevention and present techniques to overcome these challenges. METHODS: Our sample included 298 uConnect study respondents who answered a bio-behavioral survey in person and whose Facebook friend lists were downloaded (2013-2014). The study participants had over 180,000 total Facebook friends who were not involved in the study (nonrespondents). We did not observe friendships between these nonrespondents. Given the large number of nonrespondents whose networks were partially observed, a relational boundary was specified to select nonrespondents who were well connected to the study respondents and who may be more likely to influence the health behaviors of young black men who have sex with men. A stochastic model-based imputation technique, derived from the exponential random graph models, was applied to simulate 100 networks where unobserved friendships between nonrespondents were imputed. To identify peer change agents, the eigenvector centrality and keyplayer positive algorithms were used; both algorithms are suitable for identifying individuals in key network positions for information diffusion. For both algorithms, we assessed the sensitivity of identified peer change agents to the imputation model, the stability of identified peer change agents across the imputed networks, and the effect of the boundary specification on the identification of peer change agents. RESULTS: All respondents and 78.9% (183/232) of nonrespondents selected as peer change agents by eigenvector on the imputed networks were also selected as peer change agents on the observed networks. For keyplayer, the agreement was much lower; 42.7% (47/110) and 35.3% (110/312) of respondent and nonrespondent peer change agents, respectively, selected on the imputed networks were also selected on the observed network. Eigenvector also produced a stable set of peer change agents across the 100 imputed networks and was much less sensitive to the specified relational boundary. CONCLUSIONS: Although we do not have a gold standard indicating which algorithm produces the most optimal set of peer change agents, the lower sensitivity of eigenvector centrality to key assumptions leads us to conclude that it may be preferable. The methods we employed to address the challenges in using Facebook networks may prove timely, given the rapidly increasing interest in using online social networks to improve population health.

The role of commercial sex venues in the HIV epidemic among men who have sex with men.

BACKGROUND: Commercial sex venues such as bathhouses and sex clubs have long been considered important facilitators of HIV transmission among men who have sex with men in the United States. Recent probability surveys of commercial-sex-venue patrons in King County, WA that included data on behavior both within and outside these venues provide an empirical basis for the development of mathematical models to estimate the role that commercial sex venues play in the HIV epidemic. METHODS: We constructed deterministic compartmental mathematical models of HIV transmission to estimate both current incidence among King County men who have sex with men and incidence in 5 counterfactual scenarios in which commercial-sex-venues were presumed not to exist. We parameterized the models using a range of values for the proportion of commercial sex venues partnerships replaced in the absence of these venues, and the number of acts of unprotected anal intercourse per other types of partnership. Yearly attributable number was calculated as the difference between incident HIV cases in the main models and each corresponding counterfactual model. We performed extensive sensitivity analyses using Latin hypercube sampling. RESULTS: Replacement of 25% of commercial sex venue partners in the absence of these venues resulted in attributable number values near zero per year. Replacement of 50% or more of commercial sex venue partners resulted in negative yearly attributable numbers, indicating a net increase in incident HIV infections in the absence of these venues. Results of the sensitivity analyses were consistent with the main findings. CONCLUSIONS: Our findings imply that commercial sex venues contribute little to the burden of HIV among men who have sex with men in King County, WA.