The Impact of Spatial Changes on the Assessment of CCTV Effects: An Example of the Green Light Project in Detroit

The assessment of closed-circuit television (CCTV) as an infrastructure designed to improve the policing environment has gained widespread attention. The effect of CCTV is influenced not only by the time of installation, however, but also by locations, making it challenging to assess accurately from a single dimension. Existing studies have analyzed the differences in assessment results due to the period of installation, but little has been said about the sensitivity of assessment results to spatial changes. Moreover, existing assessment results rarely consider the varying degrees of influence that CCTV might have in different locations. To address these issues, we use the weighted displacement quotient (WDQ) algorithm to assess the effect of 603 CCTVs installed by the Green Light Project in Detroit from 2016 to 2019. This assessment examines the sensitivity of the WDQ algorithm to spatial changes, particularly when the radius of the target area is altered. We also optimize the matching algorithm and consider the spatial heterogeneity of CCTV’s effects in the assessment process. The results show that over 50 percent of the CCTVs installed have a diffusion of benefits on crime reduction (WDQ > 0), and the assessment results obtained using the WDQ algorithm are highly sensitive to spatial changes. These findings provide valuable insights for subsequent assessments of CCTV, and for the optimization of CCTV installation and layout to enhance their effect.