Brokenwindows Since the late 1980s, cities have bought heavily into the "broken windows" theory: the notion that an unkempt, disorderly environment breeds crime. Leaders in New York City were the first to act on the idea on a broad scale. After an aggressive campaign to clean up graffiti in the city's subway system, petty crime went down. New York Mayor Rudolph Giuliani -- along with Police Chief Bill Bratton -- used the broken windows idea in their "zero tolerance" approach to cleaning up the city in the early 1990s.

Since then, cities all over the country have jumped on the broken windows bandwagon. The theory, though, remains controversial: It's been difficult to separate the effects of cleaning up a building from a host of other factors that may also contribute to crime in a particular area.

But now, a group of Dutch researchers has conducted a series of experiments designed to test the broken windows approach.

The researchers set out to determine whether, using graffiti and other disorderly conditions, they could actually create an environment in which people were more likely to commit a crime.

They found out that they could -- in fact, they could double the number of people prepared to commit a crime.

According to the Economist :

His group's first study was conducted in an alley that is frequently used to park bicycles. As in all of their experiments, the researchers created two conditions: one of order and the other of disorder. In the former, the walls of the alley were freshly painted; in the latter, they were tagged with graffiti (but not elaborately, to avoid the perception that it might be art). In both states a large sign prohibiting graffiti was put up, so that it would not be missed by anyone who came to collect a bicycle. All the bikes then had a flyer promoting a non-existent sports shop attached to their handlebars. This needed to be removed before a bicycle could be ridden.

When owners returned, their behaviour was secretly observed. There were no rubbish bins in the alley, so a cyclist had three choices. He could take the flyer with him, hang it on another bicycle (which the researchers counted as littering) or throw it to the floor. When the alley contained graffiti, 69% of the riders littered compared with 33% when the walls were clean.

To remove one possible bias--that litter encourages more litter--the researchers inconspicuously picked up each castaway flyer. Nor, they say, could the effect be explained by litterers assuming that because the spraying of graffiti had not been prevented, it was also unlikely that they would be caught. Littering, Dr Keizer observes, is generally tolerated by the police in Groningen.

The most dramatic result, though, was an experiment that showed a doubling in the number of people who would steal when the condition of an area was disorderly:

In this case an envelope with a EUR5 ($6) note inside (and the note clearly visible through the address window) was left sticking out of a post box. In a condition of order, 13% of those passing took the envelope (instead of leaving it or pushing it into the box). But if the post box was covered in graffiti, 27% did. Even if the post box had no graffiti on it, but the area around it was littered with paper, orange peel, cigarette butts and empty cans, 25% still took the envelope.

The researchers' conclusion is that one example of disorder, like graffiti or littering, can indeed encourage another, like stealing. Dr Kelling was right. The message for policymakers and police officers is that clearing up graffiti or littering promptly could help fight the spread of crime.