Evidence-Based Policing Matrix
Neighborhood – Mares & Blackburn (2021)
Study Reference:
Location in the Matrix; Methodological Rigor; Outcome:
Neighborhoods; General; Reactive; Moderately Rigorous; No evidence of effect
What police practice or strategy was examined?
This study evaluated the Acoustic Gunshot Detection System (AGDS) in St. Louis, Missouri. The AGDS includes sensors that can detect acoustic waves produced during a gunshot incident. These waves are triangulated to locate a small spatial window for each gunshot incident which can assist police in detecting and responding to incidents of gunfire. AGDS was first deployed in St. Louis in 2008 with the devices covering three neighborhoods within the city. In 2013 the system expanded in size, covering three square miles. From July 2016 through October 2016 the AGDS system was shut down resulting in no AGDS calls for service during this period.
How was the intervention evaluated?
This intervention was evaluated using a quasi-experimental longitudinal panel study design. The researchers examined CAD data and crime reports to determine if AGDS had an impact on police response to gunshot incidents, actionable data, and gun violence. The first implementation period spanned from August 2008 through March 2013, where the AGDS covered only three neighborhoods (which served as treatment locations). The expansion period began in March 2013 (analysis used data through 2018), where treatment and control conditions were selected based on density maps of AGDS calls for service. For the gun violence analysis, control neighborhoods were matched to treatment neighborhoods based on rates of pre-experimental calls for gunshot and aggravated assault.
What were the key findings?
During the first implementation period, dispatch time was significantly faster for AGDS calls for service compared to shots fired citizen-initiated calls. However, for the expansion period, dispatch time and travel time was significantly slower for AGDS calls compared to citizen-initiated calls for shots fired. Additionally, AGDS calls resulted in less complaints (i.e., incidents uncovered) than citizen-initiated calls, with only 0.9% of AGDS calls receiving a case number compared to 73.4% for shooting calls and 7.6% for gunshot calls. There were no significant differences between treatment and control neighborhoods for crime measures during the first implementation period and the expansion period. During both these periods, there was a significant decrease in citizen-initiated reports for shots fired and shootings in treatment neighborhoods. The authors suggest further research is needed to understand why citizen-initiated calls decline, but argue this may reflect citizens not calling in less serious gun offenses.
What were the implications for law enforcement?
The authors conclude that AGDS by itself may offer little benefit to police agencies. These devices do little to improve response time to shots fired incidents, provides little assistance with uncovering crimes and criminals, and do not produce significant reductions in crime. Instead, AGDS increases the demand on police resources as they increase the call volume for gunshots incidents. Thus, while the technology is effective in detecting gunshots, responses to all of these additional calls may not be cost-effective, particularly in agencies with an already high call volume.
Where can I find more information about this intervention, similar types of intervention, or related studies?