It’s harder to climb social and professional ladders in some cities than others.
That’s according to a two-part study published earlier this week in the scientific journal Nature, which analyzed over 21 billion Facebook friendships and linked socioeconomic mobility to the relationships poor people and rich people are able to build with each other as children.
The study says children earn 20% more income in adulthood, on average, if they grow up in a city where lower- and higher-income households interact. That makes them more likely for one potential reason, it notes: Children with wealthy parents often have access to test prep courses, college counselors and established networks that lead to lucrative jobs — and those children can pass along those skills to their less fortunate friends.
That knowledge adds up. Researchers found that the effect of “social connectedness” — or meaningful interactions between rich and poor residents — was as profound as “the difference in average outcomes between a child who grows up in a family that makes $47,000 a year instead of $27,000 a year.”
Teaching children how to generate this kind of “social capital” through friendships has a ripple effect: Those skills and connections “may be particularly relevant” to building intergenerational wealth, the study notes, because they’ll eventually pass down those same lessons to their own kids.
Here’s the problem, researchers say: Such friendships don’t exist in every corner of the U.S. Out of the country’s 200 largest counties, these seven cities have the lowest rates of social connectedness in the study, starting at the bottom:
Cameron, TexasHidalgo, TexasShelby, TennesseeTulare, CaliforniaMercer, New JerseyMobile, AlabamaFresno, California
Notably, Texas and California — two of the country’s largest states — each have multiple entrants on the list. In Cameron County, the lowest-ranked large county in the study, residents have just a 24% chance of even knowing someone from a rich household. They’re also 13% less likely than people in socially connected communities to befriend someone from a different socioeconomic background.
Several factors could explain why the phenomenon is more common in some cities, says Matthew Jackson, an economics professor at Stanford and one of the study’s authors. He says it sometimes depends on the particular attitudes of specific communities, or even the size of local high schools.
Wealthier students often have tutors and access to other tools that eventually help place them in honors and AP classes. In schools with graduating classes of more than 500 kids, those wealthy students might never interact with kids on the standard education track, Jackson says.
“Those people could be attending the most diverse high school in the country, but it doesn’t mean they’re ever going to see each other,” he says. “It’s like two different high schools in one place.”
Jackson says the average income of a city’s residents is among the most reliable predictors. For example, the median household income for Cameron County is $41,200 per year, according to the U.S. Census. San Francisco, the study’s most socially connected city, has a median household income of $119,000 per year.
The goal of the study, Jackson says, is to give school administrators and city leaders more data to help them implement policies and programs that encourage interactions across socioeconomic classes. On an individual level, he adds, everyone can do a better job at getting outside their comfort zones.
“We all have really insular networks,” Jackson says. “Our own networks are probably more limited and possibly more divided than we would understand. Spending some time outside of our normal community or normal circles can help enrich that.”
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