The police measure that most consistently reduces crime is the arrest rate... Felony arrest rates (except for motor vehicle thefts) rose 50 to 70 percent in the 1990s. When arrests of burglars increased 10 percent, the number of burglaries fell 2.7 to 3.2 percent. When the arrest rate of robbers rose 10 percent, the number of robberies fell 5.7 to 5.9 percent.
During the 1990s, crime rates in New York City dropped dramatically, even more than in the United States as a whole. Violent crime declined by more than 56 percent in the City, compared to about 28 percent in the nation as whole. Property crimes tumbled by about 65 percent, but fell only 26 percent nationally.
Many attribute New York's crime reduction to specific "get-tough" policies carried out by former Mayor Rudolph Giuliani's administration. The most prominent of his policy changes was the aggressive policing of lower-level crimes, a policy which has been dubbed the "broken windows" approach to law enforcement. In this view, small disorders lead to larger ones and perhaps even to crime. As Mr. Guiliani told the press in 1998, "Obviously murder and graffiti are two vastly different crimes. But they are part of the same continuum, and a climate that tolerates one is more likely to tolerate the other."
In Carrots, Sticks and Broken Windows (NBER Working Paper No. 9061), co-authors Hope Corman and Naci Mocan find that the "broken windows" approach does not deter as much crime as some advocates argue, but it does have an effect, particularly on robbery and motor vehicle theft. They use misdemeanor arrests as a measure of broken windows policing.
Over the 1990s, misdemeanor arrests increased 70 percent in New York City. When arrests for misdemeanors had risen by 10 percent, indicating increased use of the "broken windows" method, robberies dropped 2.5 to 3.2 percent, and motor vehicle theft declined by 1.6 to 2.1 percent. But this decline was not the result of more of those involved in misdemeanors being incapacitated from further crimes by being in prison: prison stays for misdemeanors are short and only 9.4 percent of misdemeanor arrests result in a jail sentence, the authors note. Furthermore, an increase in misdemeanor arrests has no impact on the number of murder, assault, and burglary cases, the authors finds.
Corman and Mocan identify several factors that could affect crime rates. For example, the police force in New York City grew by 35 percent in the 1990s, the numbers of prison inmates rose 24 percent, and there were demographic changes, including a decline in the number of youths.
Skeptics believe that it was the economic boom of the 1990s - a "carrot" that encourages people to remain on the straight-and-narrow - that brought about the drop in crime rates in New York City and the nation. The national unemployment rate declined 25 percent between 1990 and 1999, and by 39 percent in the city between 1992 and 1999. This study shows that a single percentage point decline in the jobless rate decreases burglary by 2.2 percent and motor vehicle theft by 1.8 percent. Increases in the real minimum wage also significantly reduce robberies and murders: 3.4 to 3.7 percent fewer robberies with a 10 percent increase in the minimum wage and 6.3 to 6.9 percent fewer murders.
The police measure that most consistently reduces crime is the arrest rate of those involved in crime, the study finds. Felony arrest rates (except for motor vehicle thefts) rose 50 to 70 percent in the 1990s. When arrests of burglars increased 10 percent, the number of burglaries fell 2.7 to 3.2 percent. When the arrest rate of robbers rose 10 percent, the number of robberies fell 5.7 to 5.9 percent. In the case of murder, the decline was 3.9 to 4 percent; in the case of assault, 2 to 2.4 percent; and for motor vehicle theft, 5 to 5.1 percent.
The contribution of such deterrence measures (the "stick") offers more explanation for the decline in New York City crime than the improvement in the economy, the authors conclude. Between 1990 and 1999, homicide dropped 73 percent, burglary 66 percent, assault 40 percent, robbery 67 percent, and vehicle hoists 73 percent. The authors' model manages to explain between 33 and 86 percent of those declines.
-- David R. Francis