Thompson: In your latest paper, you described what you said might be the single most important ingredient that you’ve identified in all of your work on this subject. It has to do with friendship.
Chetty: We knew that it’s harder to rise up in more racially segregated neighborhoods. But there was always a sense that we hadn’t fully captured the picture. Social scientists have been thinking about the idea of social capital for a hundred years—including my colleague, Bob Putnam, in famous books, including Bowling Alone. We wanted to measure social capital systematically. So we teamed up with Facebook to use their data on friendships to measure what we call “economic connectiveness”— the extent to which low- and high-income folks are interacting with each other in a given place. These cross-class interactions turn out to be one of the strongest predictors of economic mobility to date. If you grow up in a place where low- and high-income folks are interacting more, you as a person growing up in a low-income family are much more likely to rise up in the next generation.
Thompson: But you found that these cross-class friendships don’t form as often as we’d think, even when rich and poor people live near each other. You call this “friendship bias.” How does it work?
Chetty: There are some places where, if you look at the lower-income folks on Facebook, they have many high-income friends. But in other places, they don’t. Two things are driving that variation. One is what we call “exposure,” which is just a simple idea that if low- and high-income folks go to different schools, attend different churches, live in different neighborhoods, they’re not going to be friends with each other.
But there’s a second force we introduce in this paper, called “friending bias.” That’s the idea that even if you and I go to the same school, even if you and I live across the street from each other, we still might not interact with each other because we might go our own separate ways and hang out with people who look like us and spend time with people who have similar interests or similar backgrounds and so forth. What we end up finding is that about half of the social disconnection in America between low- and high-income folks is coming from the lack of exposure. But the remaining half is explained by friending bias. That means even if we were to perfectly integrate every neighborhood, every college, every school, and every recreational group, we would still have half of the social disconnection between low- and high-income folks left in the United States.
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