In a somewhat angry and impulsive mood, I posted something here yesterday about crime in American cities, and the shameful lack of outrage about it. This elicited some thoughtful comments, including one by Timo Hartmann who asks:
Abbas, do you really think that in a city where thousands of illegal immigrants live on a daily basis who sleep in overcrowded houses, working on a daily basis so they can send some money home to their families, the crime problem can be solved by locking away more people? Don’t you think as soon as you lock somebody violent away there will be two or three more people who will commit crimes? Don’t you think that the presence of even more undereducated police officers would not also affect your personal freedom in a negative way?
My respective answers to your three questions, Timo, are yes, no, and no–more police will not affect my freedom in a negative way. We could argue theoretically about this until we are both blue in the face, but fortunately someone has bothered to look carefully at the data concerning the huge nationwide drop in crime in the 1990s, and tried to figure out which factors are truly effective in reducing crime rates. In a fascinating and rigorously argued forthcoming book (I happen to have an advance copy), the brilliant and non-partisan economist Steven D. Levitt of the University of Chicago writes:
The evidence linking increased punishment with lower crime rates is very strong. Harsh prison terms have been shown to act as both deterrent (for the would-be criminal on the street) and prophylactic (for the would-be criminal who is already locked up). Logical as this may sound, some criminologists have fought the logic…
…if the goal here is to explain the drop in crime in the 1990s, imprisonment is certainly one of the key answers. It accounts for roughly one-third of the drop in crime.
In fact, after carefully controlled statistical analysis of the data, Levitt shows that of the following eight most commonly cited media explanations (in order) for the crime drop, only three can be shown to have had any effect at all (can you guess which?):
Innovative policing strategies
Increased reliance on prisons
Changes in crack and other drug markets
Aging of the population
Tougher gun control laws
Increased number of police
All other explanations (increased use of capital punishment, concealed-weapons laws, gun buybacks, and others)
The correct answers are #s 2, 3, and 7. Wide-scale nationwide hiring of police in the 90s accounted for roughly 10 percent of the crime drop.
Timo also adds,
I personally believe that the reason for the high crime rate in the US compared with for example Europe is due to the huge (and growing) social gap in this country.
to which I can only say: the onus is on you to show, controlling for other factors, that this is statistically true. At this time, I simply have no reason to either confirm or deny it.
You can see a list of Levitt’s academic papers on this and other topics here. See especially, “Understanding Why Crime Fell in the 1990s: Four Factors That Explain the Decline and Six That Do Not,” Journal of Economic Perspectives 18, no. 1, (2004), pp. 163-90. I will be posting more here on Levitt’s book when it is publshed. Meanwhile, read this profile of Levitt by Stephen J. Dubner from the New York Times.