Cross-class friendships aren't so easy to come by in Miami

Miami stinks at facilitating friendships between low-income and high-income people.

• That's our takeaway from a recent study published in science journal Nature.

Why it matters: Cross-class friendships are among the strongest predictors of upward income mobility, the study suggests.

• If a kid from a poor family grew up in a neighborhood in which 70% of their friends were rich, the study found, their future incomes would be 20% higher than their counterpart who grew up without these bonds across class lines, Axios' Erica Pandey reports.
• A higher-income person might show a lower-income person how to apply for financial aid or help them land a job, one of the study's authors explained to the New York Times.

Details: Researchers looked at Facebook friendship data of 72 million people to measure "social capital" — the strengths of relationships and communities, which affect everything from education to health.

Zoom in: In Miami-Dade, the average income for adults who grew up in low-income families is $32,100 per year, the data shows, signaling low upward income mobility compared to the rest of the U.S.

• For people with low incomes in the county, just 29.3% of their friends are of high economic status.

That's because of low "exposure" and high "friending bias":

• For low-income people in Miami-Dade, 39.9% of the individuals they meet have high incomes.
• Compared to the rest of the country, low-income people here are 9.2% less likely to form friendships with high-income people they meet.

Zoom out: View our interactive chart to see how other counties stack up. (Looks like North Dakota is onto something.)