Date of Award


Degree Type


Degree Name

Master of Science in Statistics


Computer Science and Statistics

First Advisor

Natallia Katenka


The transmission of HIV/AIDS remains a great concern among people who inject drugs (PWIDs) in the United States. PWIDs are often embedded in a unique HIV/AIDS risk network via the shared use of drug equipment and risky sexual behavior. However, the characteristics of PWIDs in risk networks present challenges in a collection of network data resulting in limited studies of these networks of PWIDs. Our study employed causal inference methods applied to an observational study with dissemination to assess attitudes toward HIV/AIDS risk among PWIDs and their effect on health-seeking behaviors.

We used data from the Social Factors and HIV Risk Study (SFHR), a sociometric network study conducted between 1991 and 1993 in Bushwick, Brooklyn, New York that investigated how HIV/AIDS infection spread among PWIDs through shared sexual and injection risk behaviors. We evaluated the effects of locus of control (internal vs. external) and blame (self vs. others) attitudes separately on their own health-seeking behavior and that of other members in their risk communities. With taking dissemination of attitudes into account, four causal parameters were estimated: direct, indirect, total, and overall effects. Communities were defined to include members that were closely related via HIV risk behavior and had sparser connections with individuals outside of the community. For the health-seeking behavior outcomes, we considered receipt of study-based HIV testing result and a medical encounter within the past year. While direct effect measures direct effect of exposure on outcome behavior of PWIDs in the same community, indirect effect is the quantified measure of dissemination, which compares the outcomes of unexposed PWIDs in two different communities. Total effect is defined as the sum of direct and indirect effects and is the measure of the maximum impact of the exposure of interest. Last but not least, overall effect measures the marginal effect of exposure by comparing the potential outcomes of those exposed and unexposed regardless of communities they belong.

First, we applied a modularity-based community detection algorithm to determine communities within the SFHR network. We then employed a network-based causal inference methodology for clustered observational data. Coverage is defined as the proportion of people with internal locus of control/self-blame attribute in a community. For the direct effect, PWIDs who believe uncontrollable factors determine whether or not one gets HIV/AIDS (i.e. with external locus) were 16% less likely to receive HIV testing result when they are in 50% and 70% coverage communities (95% confidence interval (CI): -0.27, -0.06, for both communities). Also, when the coverage of people who believe controllable factors determine whether or not one gets HIV/AIDS (i.e. with internal locus) was decreased from 70% to 50%, the likelihood of receiving HIV testing result decreases 3% among those with external locus (95% CI: -0.05, -0.01), demonstrating a significant disseminated effect. Furthermore, as another significant dissemination effect, when the coverage of people with self-blame was decreased from 99% to 50%, the likelihood of having a recent medical encounter increases 27% for those with external locus (95% CI: 0.07, 0.47).

Because the SFHR study was conducted in the early 1990s, and there is a possibility that the health-seeking behavior of PWIDs has somewhat changed over time. However, our results may contribute to understanding how PWIDs attitudes and behaviors have changed over a few decades by conducting a similar analysis in more contemporary studies. The results from this study support the existence of dissemination of locus of control/blame attitudes among PWID networks. This indicates that the introduction of appropriate network-targeted interventions can bolster positive behavioral change in health-seeking among PWIDs by leveraging disseminated effects.