An Empirical Examination of the Implications of Assortative Matching on the Incidence of HIV

Using data from the San Francisco Home Health Study (SFHHS), this study in economic epidemiology analyzes the degree to which the incentives to avoid HIV infection result in infection-dependent (assortative) matching patterns based on HIV status. The incidence implications induced by such matching are compared to infection-independent matching, an implicit assumption in some models within epidemiology. The authors estimate that an HIV-positive individual is more than twice as likely as an HIV-negative individual to have an HIV-positive partner, and that this results in a decrease in HIV incidence of about one-third over the predictions implied by standard epidemiological models. In these data, the agreement can be shown to be due to initial matching, not to subsequent infection.