The objectives of this study were to 1) determine whether crime-reduction effects of increased police patrols in hot spots were dependent on the "hard" threat of immediate physical arrest, or whether "soft" patrols by civilian (but uniformed) police staff with few arrest powers and no weapons can also reduce crime; 2) whether the number of discrete patrol visits to a hot spot was more or less important than the total minutes of police presence across all visits; and 3) whether effects based on counts of crime would be consistent with effects on a Crime Harm Index outcome.
Overall, the study found that a crime reduction effect of extra patrols in hot spots was not conditional on "hard" police power. Even small differences in foot patrols showing the "soft power" of unarmed paraprofessionals, holding constant vehicular patrols by police constables, were causally linked to both lower counts of crimes and a substantially lower crime harm index score. Correlational evidence within the treatment group suggests that greater frequency of discrete police community service officer (PCSO) visits may yield more crime reduction benefit than greater duration of those visits, but RCTs are needed for better evidence on this crucial issue. The study randomly assigned 72 hot spots into 34 treatment units and 38 controls. Treatment consisted of increases in foot patrol by uniformed, unarmed, Police Community Support Officers (PCSOs) without weapons and with few arrest powers beyond those of ordinary citizens. GPS-trackers on every PCSO and Constable in the city measured all patrol time in all hot spots. Standardized mean differences (Cohen's d), OLS regression model, and Weighted Displacement Quotient were used to assess main effects, to model the interaction effect of GPS data with treatment, and to measure the diffusion-of-benefits of the intervention, respectively. Outcomes included counts of incidents as well as the Cambridge Crime Harm Index. As intended, patrol visits and minutes by Police Constables were equal across the treatment and control groups. The sole difference in policing between the treatments groups was in visits to the hot spots by PCSOs, in both the mean daily frequency of discrete visits (T=4.65, C=2.66; p being less than or equal to .001) and total minutes across all visits (T=37.41, C=15.92; p being less than or equal to .001), approximately two more 10-minute visits per day in treatment than in control. Main effect estimates suggest 39 percent less crime by difference-in-difference analysis of reported crimes compared to control conditions, and 20 percent reductions in emergency calls for service compared to controls. Crime in surrounding areas showed a diffusion of benefits rather than displacement for treatment hot spots compared to controls. A "Reiss's Reward" effect was observed, with more proactive patrols predicting less crime across treatment hot spots, while more reactive PCSO time predicted more crime across control hot spots. Crime Harm Index estimates of the seriousness value of crime prevented ranged from 85 to 360 potential days of imprisonment in each treatment group hot spot (relative to controls) by a mean difference of 21 more minutes of PCSO patrol per day, for a potential return on investment of up to 26 to 1. (publisher abstract modified)