Experimental evidence for the Broken Window Theory
In the late 80's, New York experienced a high rate of violence and crack was everywhere. In 1985 when George L. Kelling, coauthor of the article "Broken Windows", was hired as a consultant to the New York City Transit Authority, the subway was awfull. Kelling implemented new measures. He made every graffiti disappear and cleaned every station. Day after day after day, new graffitti would be made in the night and removed during the day, until oneday the new policy started to be successful and graffiti progressively disappeared. Mayor and police department of New York also employed the same method, they implemented a zero tolerance policing with easier arrestee procedure. Police started enforcing the law very strictly, against subway fare evasion, public drinkers, urinators, and the like. The rates of both petty and serious crime fell suddenly and significantly.
New York crime and drug decline is one of the best example of a successful implementation of the Broken Window Theory (BWT). BWT states that signs of disorder, like graffiti, dirty streets, broken windows… induce more disorder. Not only more graffitti and other petty crimes, but also more serious crimes like murder, robbery, etc. Consequently, removing the minor signs of disorder is thought to induce a decrease in the amount of more serious crimes.
Figure: Minor signs of disorder in Paris, France (author: Jean-noël Lafargue).
The BWT has been implemented in many cities around the world, with some success, but until now, the causal arrow leading from minor crime to more serious ones has remained highly speculative.
In a recent paper, Kees Keizer, Siegwart Lindenberg and Linda Steg conduct insightful and delightful field experiments to assess the BWT. I'll detail just one example to give you the flavour of the six experiments. In one setting they looked at whether individuals would steal an envelope visibly containing a five euro note. "The white (addressed) window envelope sticking out of a mailbox (situated in Groningen) was very noticeable for everyone approaching the mailbox, and it was clearly visible that the envelope contained a €5 note". In the baseline condition the mail box and the ground surrounding it were clean. In one test condition the mail box was covered with graffitti and in another the ground was covered with litter.
The results were quite dramatic, the rate of robbery doubled between the baseline and the "disorder" conditions! In the baseline condition, 13% of passer-bys stole the envelope, with graffitti this rate raised to 27% and with litter to 25%.
The authors conclude: "There is a clear message for policymakers and police officers: Early disorder diagnosis and intervention are of vital importance when fighting the spread of disorder. Signs of inappropriate behavior like graffiti or broken windows lead to other inappropriate behavior (e.g., litter or stealing), which in turn results in the inhibition of other norms (i.e., a general weakening of the goal to act appropriately). So once disorder has spread, merely fixing the broken windows or removing the graffiti may not be sufficient anymore. An effective intervention should now address the goal to act appropriately on all fronts."
Abstract of the paper:
Imagine that the neighborhood you are living in is covered with graffiti, litter, and unreturned shopping carts. Would this reality cause you to litter more, trespass, or even steal? A thesis known as the broken windows theory suggests that signs of disorderly and petty criminal behavior trigger more disorderly and petty criminal behavior, thus causing the behavior to spread. This may cause neighborhoods to decay and the quality of life of its inhabitants to deteriorate. For a city government, this may be a vital policy issue. But does disorder really spread in neighborhoods? So far there has not been strong empirical support, and it is not clear what constitutes disorder and what may make it spread. We generated hypotheses about the spread of disorder and tested them in six field experiments. We found that, when people observe that others violated a certain social norm or legitimate rule, they are more likely to violate other norms or rules, which causes disorder to spread