Perhaps the best single indicator of a metropolitan area’s economic mobility is the percentage of black people living there. The greater the share of black people, the less likely it is that a poor kid — black, white, or anything else — will make more money than their parents.

At a time of anxiety in the US about economic mobility, the data show a stark racial, and therefore regional — black people live disproportionately in the Southeastern US — factors that work at keeping poor people poor and rich people rich. Economic mobility is not a uniform, universal problem in this country.

Judging by the 50 largest metro areas in the US, the percentage of black people had a correlation of 56% with a metro’s economic mobility.

Scott Winship, a fellow at the Manhattan Institute who’s studied economic mobility, emphasized family structure as the explanation for low mobility rates in cities with large black populations.

“African American kids are much more likely to be born to a single parent than White kids are.

theres a lot of argument about whether that’s a causal relationship, but I think it is.” Still, “I don’t know that anyone knows exactly what’s going on,” he said.

A metro’s sprawl was nearly as good a predictor, at 54% — the greater the sprawl, the lesser the mobility. Just below that, at 47%, was a metro’s per capita personal income, a measure of how much money flows through a city relative to the size of its population. More money correlated with more mobility.

The stats on economic mobility are from the National Bureau of Economic Research’s recent paper on the subject. The other factors — like sprawl, and the percentage of a metro’s population that is black — are data dating from 1980, because that’s around when the subjects of the mobility research were born. The data is all directly from the census, except for the measure of metropolitan sprawl, which was done at Boston University, and the measure of economic segregation, done at Pew. Both used census numbers.

Poverty rates among families were far behind, with a 34% correlation — metros with lots of poverty tended to have lower mobility.

Next came the percentage of people of “spanish origin,” as the 1980 census put it, with a 28% correlation — a positive one! Metros with more Latinos tended to have higher rates of economic mobility.

Last, among the data reviewed, was economic segregation. There was basically no correlation whatsoever between whether rich and poor rubbed shoulders as neighbors — or not — and whether a poor kid grew up to do better than his parents.

None of this means that any of these factors directly drive economic mobility up or down. It only means that where you find one, you often find the other.

And on a different note, this data is largely unsurprising. Sprawl, especially among the left, is thought to be a bugaboo of opportunity. The poor are forced into long commutes in expensive cars, and easily left stranded far from the jobs they’d like to have, the thinking goes. Paul Krugman concedes that thinking could be wrong.

“You can easily think of reasons for spurious correlation: sprawl is associated with being in the sunbelt, with voting Republican, with having weak social safety net programs,” he blogged. “Still, it’s striking.”

The same holds true for the relationship between large black populations and low mobility: black people live disproportionately in the sunbelt, with those same Republicans and weak social safety nets that Krugman noted.

Krugman’s colleague at the Times, David Leonhardt, also pointed out that the overlap between large black populations and low mobility wasn’t just about black mobility — the children of poor white people also tended to stayed poor in cities with large black populations.

As for the happy correlation between large Latino communities and high economic mobility, Winship at the Manhattan Institute suggested it was more an immigration story: Latinos opened the doors where opportunity knocked.

“Maybe the high Hispanic numbers are a marker of cities that are doing well” — even before Hispanic people arrived, Winship said.