Within a 90 day time period that started on February 8 and ran through May 8, 2011, Sergeant Renee Mitchell of the Sacramento [California] Police Department designed a research methodology that she hoped would test out the Koper curve theory of hot spot policing. This theory proposes the notion that certain specific locations or neighborhoods can harbor an unequal distribution of crime in comparison to other locations in that same area. Additionally, this theory goes on to explain that police officers who are highly visible in these areas for 12–16 minutes can cause a reduction in crime as well as calls for service (CFS) within that hot spot.1 With her knowledge and experience in evidence-based policing and hot spot policing, Sergeant Mitchell used her training to conduct research in order to find if such a theory proved true within Sacramento.
The Research Design
Hot spots were chosen and rank ordered as separate areas of interest by identifying those areas with the highest numbers of Part 1 crimes (i.e., homicide, aggravated assault) based on the Uniform Crime Reports statistics as well as how many CFS would come to the police department regarding these Part 1 crimes. Forty-two hot spots were selected and limited to 100 block increments (also called a “micro-place”)(see Figure 1). Additionally, due to the small sample size, the 42 hot spots were paired in order to increase statistical power in the research design. By starting with the two highest ranked hot spots and working to the lowest ranked, a computerized random number generator assigned one spot to the treatment (hot spot policing group), while the other was assigned to the control group (routine patrol duties performed). In order to control for any possible variations due to this pairing, the Part 1 crimes, number of CFS, and geography of the hot spot were all similar within the pairs.
With the 42 hot spots selected, it was time to bring in the patrol officers who would be key in taking part in the study. Through random selection, the officers were assigned to the hot spots that they would need to patrol for 90 days. The experiment also required the officers to be proactive in their patrol. It was suggested that they go to their randomly assigned hot spot for 12–16 minutes and be highly visible in the community, while also taking time to talk to the public as well. Additionally, the officers were asked to visit each hot spot in their assigned district every 2 hours. The Koper curve theory claims that these 12–16 minutes of hot spot policing reduce crime for approximately 2 hours afterward in that particular area.2 By replicating these conditions fully, the Sacramento PD experiment wished to test this theory in its entirety.
At the end of the 3 month experiment, it was discovered that Part 1 crimes decreased by 25 percent in the treatment hot spot areas, while the hot spots in the control areas had their Part 1 crimes increase by 27.3 percent. It is important to note here that the officers in the control group were still patrolling and conducting their regular policing duties as usual, it is just that the treatment group of officers were performing those duties in a different way through hot spot policing. The results also found that CFS decreased by 7.7 percent in the treatment areas, while CFS increased by 10.9 percent in the non-treatment areas. Variables such as temperature and precipitation levels remained relatively the same as in previous years.
Officer productivity was found to have increased as well due to hot spotting. Regular duties such as traffic stops, arrests, officer-initiated calls, etc., did not decrease in comparison to the year prior to the experiment (2010). And although subject stops did decrease, it was a trend that lined up with two other districts whose subject stops also decreased.
Officer Pro-activity Tables:
Table 1: “An Example of Incorporating Science into Policing: A Hot Spots Experiment in the Sacramento Police Department”. Interview with Sergeant Renee Mitchell; Sacramento Police Department and Powerpoint (Slide 10). May 9, 2012.
In regards to displacement, the department looked at a two block radius as the “buffer zone” surrounding each of the hot spots to see if any Part 1 crime increased in these areas. It was discovered that Part 1 crime and CFS did increase in two treatment areas, but decreased everywhere else. After further research, it was revealed that a brand new department store had just been built near these two treatment areas that could explain the increase in Part 1 crime. Overall, displacement was not a significant issue.
Additionally, through a cost-benefit analysis, it was found that the police department saved close to $300,000 in costs associated with crime by hot spotting. By using an average of the three lowest cost Part 1 crimes and multiplying it by the lowest Part 1 crimes that were eliminated during the 90 day experiment, the Sacramento PD discovered cost savings of $289,550.3
It is a huge step forward for law enforcement agencies when best practices in policing can be backed up by empirical studies. In a time of increased budget cuts and limited resources, it is crucial to discover and promote best practices that can be proven to be more effective in the field. The Sacramento PD and Sergeant Mitchell have done something impressive in bringing academic research into the field of policing in order to help our law enforcement officers do their jobs more efficiently. Providing the right training and education to officers who are interested in taking part in research and then coming back to the department to implement a study and/or train other officers in research methodologies would be a great benefit to any law enforcement agency.
Sergeant Mitchell has conducted an immensely important experiment that can not only increase her department’s efficiency, but also provide an excellent example to other police departments nationwide in the importance of supporting their best practices through empirical research.4
For more information about this experiment in hot spot policing, you may contact Sergeant Renee Mitchell at: firstname.lastname@example.org
The COPS Office