What's Known About Deterrent Effects of Police Activities
Several techniques have been used to estimate effect of police activities on incidence of crime: (1) cross-sectional analysis of reported crime rates compared with resources devoted to police functions, (2) longitudinal analysis of a time series of crime incidence where police deployment or operations changed over time, and (3) experimental manipulation of police activities. Nearly every study has one or more faults, such as failure to distinguish between true and reported crime rates, failure to specify or maintain the experimental conditions, apparent errors in the data, or confusion between cause and effect. This review indicates that most studies are consistent with the view that a substantial increase in police activity will reduce crime for a period of time, but in the real world increases in police manpower tend to follow increases in crime. The magnitude and duration of deterrence effects are essentially unknown.