Whose Neighborhood Is It?

On June 25, 1974, suburban residents of Detroit won their four-year battle to overturn court-ordered busing of black city students across county lines into their schools.

In a key 5-4 Supreme Court decision, Milliken v. Bradley, Chief Justice Warren Burger declared that 41 white suburban governments had not committed “significant violations” of the Constitution.

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The victory in Milliken was based on the assumption that African-Americans would be bused in, not that they would be living next door. What was not anticipated was a black exodus from Detroit as African-Americans capitalized on new housing laws to move away from the decaying city. The white response to this migration? Flight from inner-ring suburbs.

Southfield, Mich., for example, which had been 0.7 percent black in 1970, by 2010 had become 70.3 percent black, and its schools nearly 95 percent black. {snip}

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These suburban Detroit communities provide a case study in what has come to be called the “tipping point,” the point at which whites begin to leave a residential locale en masse as African-Americans or other minorities move in.

This phenomenon puzzled Thomas Schelling, a professor emeritus of economics at Harvard and a Nobel Laureate, who was struck by the lack of stable integrated communities. In 1971, he began work on a mathematical theory to explain the prevalence of racial segregation in a paper titled “Dynamic Models of Segregation,” published in the Journal of Mathematical Sociology.

Schelling’s famous thesis has been carefully summarized by Junfu Zhang, an economist at Clark University. Zhang writes:

Schelling’s most striking finding is that moderate preferences for same-color neighbors at the individual level can be amplified into complete residential segregation at the macro level. For example, if every agent requires at least half of her neighbors to be of the same color―a preference far from extreme―the final outcome, after a series of moves, is almost always complete segregation.

In other words, residential segregation can emerge even if initial preferences are very slight.

According to Schelling, Zhang writes,

in an all-white neighborhood, some residents may be willing to tolerate a maximum of 5 percent black neighbors; others may tolerate 10 percent, 20 percent, and so on.

The ones with the lowest tolerance level will move out if the proportion of black residents exceeds 5 percent. If only blacks move in to fill the vacancies after the whites move out, then the proportion of blacks in the neighborhood may reach a level high enough to trigger the move-out of the next group of whites who are only slightly more tolerant than the early movers. This process may continue and eventually result in an all-black neighborhood.

Similarly, an all-black neighborhood may be tipped into an all-white neighborhood, and a mixed-race neighborhood can be tipped into a highly segregated one, depending on the tolerance.

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David Card, a Berkeley economist, working with Alexandre Mas and Jesse Rothstein, both Princeton economists, studied neighborhood change from 1970 to 2000, and found:

Most major metropolitan areas are characterized by a city-specific ‘tipping point,’ a level of the minority share in a neighborhood that once exceeded sets off a rapid exodus of the white population.

The tipping point, Card and his collaborators note, has been slowly but steadily rising, from an 11.9 percent minority share in the period from 1970-80, to 13.5 percent in 1980-90, to 14.5 percent in 1990-2000.

A tipping point in the 13 to 15 percent range means that “a neighborhood can remain stable with a moderate minority share,” according to Card. He and his coauthors conclude “that tipping points are semi-stable, and that neighborhoods can retain an integrated character so long as they remain below the tipping point.”

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