CITIES WERE A MISTAKE:

It takes a neighborhood to cut crime (Tim Harford, February 27, 2008, Sac Bee)

Could economics say anything about what makes our neighborhoods defend us or abandon us? I discovered that it could. Economists can now tell us why neighborhoods go through dramatic transitions from dangerous to safe or rich to poor; they have established a clear link between urban architecture and crime; they can even shed some light on whether local crime is contagious. And they can tell us what difference law enforcement really makes when the streets are peopled by those who try to kill for no reason.

Cities frequently fall into a sharply defined patchwork of thriving areas and struggling ones, often divided along racial lines. It is easy to see this as the result of bitter prejudice. But the Nobel Prize-winning economist Thomas Schelling proved decades ago that the motivations that lead to segregation may be less entrenched than you might suppose.

In the days before computer simulations, Schelling demonstrated his theory with a game played with randomly distributed pennies and nickels on a checkerboard. He invented a simple rule for how the coins moved: A nickel could be happy as long as it was touching two or more other nickels. But if it touched only one other nickel, it would hop elsewhere, leaving its former neighbor isolated. One coin after another would move in a chain reaction. Schelling's game seemed to make possible a mixed checkerboard, but the result was always segregation.

The lesson? Even if everyone were comfortable living in a mixed neighborhood, extreme segregation -- by race, class or income -- could still emerge from people's mild preferences not to be outnumbered.

Countless individually rational decisions can snowball into a socially regrettable outcome.

Schelling's successors are exploring ways in which societies can "flip" from bad situations to good ones. City streets can be unsettlingly empty or reassuringly thronged with passers-by. The safer and livelier the streets feel, the safer and livelier they become.

This virtuous circle means a small catalyst can transform a neighborhood from struggling to thriving.

Architecture matters, too, something we feel intuitively but find hard to prove or quantify. Think of high-rise apartments. Do they make a city safer by packing more people into an area and giving the streets a greater bustle? Or are cities safer if most buildings are low-rise, so people feel a connection to the street? Two new-wave economists, Edward Glaeser of Harvard and Bruce Sacerdote of Dartmouth, matched crime figures with data on building height and discovered that the residents of high-rise apartments are much more likely to be crime victims, specifically street crime. The effect remains similar after statistically adjusting for poverty, demographics and public housing: It's the height of the building itself that matters.

These insights apply to numerous issues, not least why urban intellectuals advocate the politics of atomization and dependency on the state--since it just reflects the lives they lead.

Posted by Orrin Judd at February 28, 2008 12:56 PM