Evidence-Based Policing Matrix
Micro Places – Chainey et al. (2023)
Study Reference:
Location in the Matrix and Methodological Rigor:
Micro places; Focused; Proactive; Moderately Rigorous; Mixed effects
What police practice or strategy was examined?
This study evaluated a hot spot policing intervention, designed to reduce robberies and thefts from pedestrians, implemented in four different Argentinian cities: La Plata, Morón, Santa Fe, and Tres de Febrero. The authors identified the street segments across each city that accounted for 25% of all robberies and thefts. Foot patrols consisting of two officers each were implemented in these segments, with each foot patrol route being limited to 4-8 segments each. Foot patrols were distributed across these four cities based on the number of hot spot patrol routes and the times crime was occurring in those hot spots. Each route was patrolled for 1 hour, with the officers performing multiple circuits of the single route before moving on to another route. Officers were trained on hot spot policing and were encouraged to remain visible during their patrols. Officers were also encouraged to talk to individuals they encountered during their patrols and perform their law enforcement duties normally. The intervention began on October 1, 2017 (except for in Santa Fe, where the start was delayed to November 1, 2017) and operated for a period of six months.
How was the intervention evaluated?
The impact of the intervention was evaluated using the Weighted Displacement Difference (WDD) Z statistic and difference-in-differences regression. Treatment hot spots were matched with control units using propensity score matching (with the exception of the Santa Fe site) on the number of robberies and thefts, population, land use, and social deprivation. Street segments located within 200 meters of the treatment segments were excluded from the pool of possible controls to minimize the possibility of contamination. Due to the rotation routes officers took between patrol routes, the authors suggest that contamination was likely, so they evaluated possible crime displacement by examining the impact of the intervention on assaults and vehicle crimes, two offenses that they hypothesized would not be affected by the hot spot patrols in the treatment areas because they occurred at different times than robberies and thefts from pedestrians (these data were not available for the city of Santa Fe). The authors used weekly datasets for each treatment and control unit and crime type, aggregating the counts of crime in the period before and after the intervention. The observation period for La Plata, Morón, and Tres de Febrero lasted from January 31, 2016 to April 14, 2018, and the observation period for Santa Fe lasted from January 6, 2016, to May 1, 2018. Finally, the authors also included analyses comparing the differences in impacts seen in the first half (3 months) of the intervention to the second half to gauge whether program fatigue played any role in the effectiveness of the intervention over time.
What were the key findings?
The authors note that the weekly incidence of crime in some cities was low or zero, so finding potential decreases were limited by this floor effect. Many of the findings reported by the authors for each individual city were not significant, but when pooling robberies and thefts across the four cities, they found a 14% decrease in robbery and theft for the complete 6-month period of the intervention. When comparing the first and second halves of the intervention, the authors only report a significant 20% reduction in robberies and thefts during the second three-month period. The authors did not find a significant change in the level of assaults or vehicle crime over the duration of the intervention, leading them to conclude that the hot spot policing intervention did not cause crime displacement or diffusion of benefits.
What were the implications for law enforcement?
Research teams performed site visits to observe the intervention, attended monthly meetings with representatives from the city before and after the intervention, and took systematic notes to capture details about the process. They found that in La Plata and Tres de Febrero, which had higher quality project planning, program implementation, and program monitoring, also experienced the most significant decreases in robbery and theft. The notes detailed problems with initial implementation and poor commitment, as well as a lack of clear management and supervision in Santa Fe and Morón, which may have undermined the intervention. With this in mind, the authors propose using qualitative assessment tools to improve the overall evaluation.
Where can I find more information about this intervention, similar types of intervention, or related studies?