a1 Department of Economics, Stanford University, Stanford, CA, USA; Santa Fe Institute, Santa Fe, NM, USA; and CIFAR, Canada (e-mail: email@example.com)
a2 Department of Economics, Universidad Pablo de Olavide, Sevilla, Spain and CORE, Université catholique de Louvain, Louvain-la-Neuve, Belgium
We study the diffusion of an idea, a product, a disease, a cultural fad, or a technology among agents in a social network that exhibits segregation or homophily (the tendency of agents to associate with others similar to themselves). Individuals are distinguished by their types—e.g., race, gender, age, wealth, religion, profession—which, together with biased interaction patterns, induce heterogeneous rates of adoption or infection. We identify the conditions under which a behavior or disease diffuses and becomes persistent in the population. These conditions relate to the level of homophily in a society and the underlying proclivities of various types for adoption or infection. In particular, we show that homophily can facilitate diffusion from a small initial seed of adopters.