Network Structure and the Speed of Learning: Measuring Homophily Based on its Consequences

Abstract

Homophily is the tendency of people to associate relatively more with those who are similar to them than with those who are not. In Golub and Jackson (2010a), we introduced degree-weighted homophily (DWH), a new measure of this phenomenon, and showed that it gives a lower bound on the time it takes for a certain natural best-reply or learning process operating in a social network to converge. Here we show that, in important settings, the DWH convergence bound does substantially better than previous bounds based on the Cheeger inequality. We also develop a new complementary upper bound on convergence time, tightening the relationship between DWH and updating processes on networks. In doing so, we suggest that DWH is a natural homophily measure because it tightly tracks a key consequence of homophily -- namely, slowdowns in updating processes.

Keywords: networks, learning, diffusion, homophily, friendships, social networks, random graphs, convergence, speed of learning, convergence rate

JEL Classification: D83, D85, I21, J15, Z13