Social networks and unobserved heterogeneity in risk for AIDS

As a sexually transmitted disease, AIDS spreads along social networks; consequently, it is reasonable to propose to utilize these networks in teaching people to avoid practices that put them at increased risk of contracting AIDS. Most obviously, homosexual men are both at relatively high risk of contracting AIDS, and in many urban areas have well crystallized community structures and high social connectivity. We present evidence suggesting that using such social networks can have the unanticipated consequence of reaching a set of men who are at relatively low risk. Evidently, there is great unobserved heterogeneity among the population in terms of risk, and while this heterogeneity is not captured by conventional measures of risk behavior, it is closely linked to network processes.