A tale of two experiments
Kansas City ExperimentThe first experiment was done in 1972 by the Kansas City Police Department. The Department wanted to find out whether their routine preventive patrol was really effective in reducing crime, and ran the following experiment. Fifteen police beats in the city were divided into five groups of three beats. Each group was chosen based on observable demographic, economic, and criminal characteristics so that the three police beats within each group were highly comparable to each other. Then, within each group, the Department randomly assigned one police beat as “control”, another as “reactive” and the third as “proactive”.In the police beats assigned to the control group, police performed their routine patrol as usual. For the reactive group, police stopped preventive patrol altogether and only responded to calls for service. For the beats in the proactive group, the department significantly increased police visibility by sending out a lot more preventive patrol than usual. The department closely monitored weekly crime data so that they would stop the experiment in case of a noticeable crime increase from the reactive group. Fortunately this problem did not happen during the 12 month span of the experiment.Surprisingly, the comparison between crime rates from the three groups revealed that additional police patrol did little to reduce crime, as crime rates from the three groups were very much similar. The finding led many researchers and policymakers to question the effectiveness of preventive police patrol for many years. For example, Carl Klockars (1983) argued that “it makes about as much sense to have police patrol routinely in cars to fight crime as it does to have firemen patrol routinely in fire trucks to fight fire.”
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Economics of Crime
Minneapolis ExperimentRecent advances in computing and mapping technology enabled researchers to easily visualize and analyze spatial patterns of crime. The spatial analysis consistently shows that crime is heavily concentrated in a small segment of “hotspots”. Just like how a small number of high-risk individuals are responsible for a disproportionately large share of crimes, few addresses and street corners account for a bulk of crimes in a city.For example, criminologists Lawrence Sherman, Patrick Gartin, and Michael Buerger found that more than half of all police calls in Minneapolis originated from just 3 percent of street addresses, and that no police car was ever dispatched to about 40 percent of the street addresses and street corners during a calendar year. What would happen if police spends more patrol hours in these crime hotspots? Would this lead to a substantial reduction in crimes? Clearly, it should be a lot easier to significantly increase police presence in a few street corners and addresses than the entire police beat.In order to test whether this hotspot-based intervention would yield a different result from the earlier beat-based experiment, criminologists Lawrence Sherman and David Weisburd designed and implemented the following randomized experiment in Minneapolis. With an endorsement and cooperation from the city government, Sherman and Weisburd identified 110 crime hotspots in the city and randomly assigned them into two groups. Hotspots in the control group received the usual level of police patrol, and those in the experimental group received about twice as many patrol hours as the control group.After the experiment was concluded, Sherman and Weisburd compared crime rates between the two groups, and found that hotspots in the experimental groups had roughly 10 percent fewer calls for service. Their finding led to renewed academic and policy discussions on the use of preventive patrol as a potential crime-fighting tool. Similar experiments from Boston, Baltimore, Seattle, and Vancouver also support that hotspot-based preventive patrol can lead to a significant reduction in crime.
- Kelling, George L., Tony Pate, Duane Dieckman, and Charles. E. Brown. 1974. The Kansas City Preventive Patrol Experiment: A Summary Report. Washington, DC: Police Foundation
- Klockars, Carl. Thinking about Police. New York: McGraw-Hill, 1991.
- Sherman, Lawrence W., Patrick R. Gartin, and Michael E. Buerger. “Hot Spots of Predatory Crime: Routine Activities and the Criminology of Place.” Criminology 27.1 (1989): 27-56.
- Sherman, Lawrence W., and David Weisburd. “General Deterrent Effects of Police Patrol in Crime “Hot Spots”: A Randomized, Controlled Trial.” Justice Quarterly 12.4 (1995): 625-648.
Economics of Crime
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