On the occasion of Bill Bratton's return as New York City police commissioner (and he was Boston's commissioner first, you Hub-haters), Pacific Standard's Lauren Kirchner notes that the "broken windows" theory has lost some of its shine since Bratton first served under Rudy Giuliani. The gist of the theory is that when low-level crimes (graffiti, subway fare evasion, etc.) go unchecked, the atmosphere of decay emboldens criminals to commit more frequent and more serious offenses.
Kirchner writes that academics have dialed back the praise for the Giuliana-era crackdown on taggers and panhandlers:
Many critics of broken windows have pointed out that violent crime fell in New York at the same period of time as unemployment dropped and the economy strengthened — surely factors at least as important as the disappearance of squeegee guys. An influential 2006 article in the University of Chicago Law Review by Bernard Harcourt and Jens Ludwig argued that the falling-crime trend in 1990s New York ran parallel to the natural waning of the crack epidemic that had ravaged the city in the years before. Other researchers found from their experiments that disorder does not cause crime; rather, disorder and crime co-exist, and are both caused by the same social and economic factors.
The broken-windows theory was certainly overhyped. But perhaps it was also a successful bluff, or self-fulfilling prophecy.
The thing is, it's tough to convince people that crime is going down. Statistics have no chance against friends' anecdotes and scare stories on TV. But the broken-windows theory was a powerful rejoinder to skeptics of falling crime rates. Instead of throwing numbers at someone, you could say, "Look! There are no more squeegee guys on that corner! And there's no graffiti on the side of that building! You can see that things have changed!" I lived in New York in the mid 1990s, and most residents accepted this theory. And so they continued to live in the city, and they went out more often at night, and they took the subway instead of cabs, and there were more people on the streets to watch out for each other and discourage crime.
We know now that the broken-windows theory was simplistic, and it fudged cause and effect, but it turned out to be a powerful propaganda tool for New York and other major cities. In retrospect, it may not have changed the behavior of would-be criminals as much as it changed the perception of law-abiding citizens. In this case, the rule of unintended consequences worked out pretty well.