How do network evolution and population structure jointly shape social outcomes?
Network externalities (where the value of adopting a behavior or practice is higher if you are connected via networks to those that have already adopted the behavior or practice) are a mechanism that exacerbates social inequality under the condition of homophily (where advantaged individuals poised to be primary adopters are socially connected to other advantaged individuals). Network externalities exist on many outcomes, ranging from the adoption of technological innovations, educational pursuits, and migration decisions.
Prior studies using agent-based models of diffusion (adoption of a new behavior or practice) often rely on a real-life population for empirical illustration and, thus, do not consider how counterfactual levels of consolidation might mediate the link between homophily and inequality in diffusion. Consolidation is a compositional characteristic of populations or social settings that refers to the extent to which multiple attributes are correlated at the context-level (i.e., if most low-status individuals are minorities and most high-status individuals are majorities, this is a high level of consolidation).
“Homophily, under low consolidation, is not sufficient to exacerbate existing differences in adoption probabilities across groups... In contrast, the combination of high homophily and high consolidation exacerbates inequality.”
Using an agent-based model, we find that the link between homophily and segregated social ties (and thus differential diffusion outcomes) are contingent on high levels of consolidation.
Under low consolidation, in which social dimensions are largely independent, increasing homophily is not sufficient to segregate social networks. In fact, under low consolidation, high homophily is helpful to create overlapping social ties, or "wide" social bridges, across which diffusion occurs. In other words, homophily, under low consolidation, is not sufficient to exacerbate existing differences in adoption probabilities across groups and can even end up alleviating intergroup inequality (Figure 8A, above) by facilitating diffusion.
In contrast, under high consolidation, low and moderate levels of homophily produce the least inequality in adoption (as shown in Figure 8B, above). Under the conditions of high consolidation, homophily exacerbates inequality in diffusion outcomes due to network externalities.
Our paper can be found here: https://journals.sagepub.com/doi/abs/10.1177/00491241211014237
Zhao L, Garip F. Network Diffusion Under Homophily and Consolidation as a Mechanism for Social Inequality. Sociological Methods & Research. May 2021.
We are happy to provide the replication package for the simulations used in this paper, below.