General deterrent effects of police patrol in

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SUMMARY After the Kansas City experiment, researchers and academics placed very little value on the ability of preventative routine patrols to deter crime. However, further examination of the Kansas City Experiment revealed shortcomings in methodology, in particular a statistical bias towards a null hypothesis and a measurement problem in determining the dosage of patrols for a specific area. This randomized controlled experiment addressed these shortcomings by determining the effect of police patrols on very small clusters of high-crime addresses in the city of Minneapolis. This "hot spot" oriented approach indicates that police patrols of sufficient duration can have a moderate deterrent effect on crime.

DATA AND METHODS This study took place in Minneapolis, MN. Selection of hot spots for the experiment began with an examination of data files on all dispatched calls for police service citywide to identify address clusters with 20 or more "hard calls", or offenses such as holdup alarms, auto theft, assault and rape, and substantial "soft calls", or offenses such as public drunkenness, disturbances, or fights. Computer mapping of this data revealed 420 address clusters available for study. After visual inspection of hot spots and screening for size, location, and nearness to other hot spots, 110 hot spots were selected for this study and randomly assigned to either the experimental or control group. For the 55 hot spots assigned to the experimental group, officers increased patrol presence to a target duration of 3 hours per day. Patrol logs and independent observation of the targeted hot spots were used to validate the duration of patrol presence per day in each hot spot. The impact of the increased patrol presence was measured by citizen calls concerning crime and independent observations of crime at the selected hot spots.

FINDINGS This study found a clear, if modest, general deterrent effect of substantial increases in police presence in crime hot spots. Although the findings were not sufficient to support a general deterrent effect of police presence throughout the community, they do support a place-specific "micro-deterrence" in the hot spots which received additional patrols.

IMPORTANCE OF THIS STUDY The Sherman and Weisburd study began a series of subsequent studies on hot spot policing which ultimately led to the National Academy of Sciences, National Research Council on the Fairness and Effectiveness of Policing to deem this tactical approach to be one of the most evidence-based approaches that police can take to reduce crime.

Sherman, L.W., & Weisburd, D. (1995). General deterrent effects of police patrol in crime "hot spots": A randomized, controlled trial. Justice Quarterly, 12:4, 625-648.

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