Crime Diffusion and Displacement: Measuring the Side Effects of Police Operations*

Abstract

In 2005, the Camden, New Jersey, Police Department responded to concerns about crime with a series of high-visibility, directed, uniform patrol deployment initiatives. The department deployed extra resources on overlapping shifts into hotspot areas to counteract trends in burglary, violence, and drug crime. In situations such as this, where police employ directed and geographically targeted enforcement initiatives, both police and the public are often concerned about displacement; however, until recently no standard tool for measuring displacement was available. The weighted displacement quotient, despite some acknowledged methodological concerns, represents for the first time a systematic approach to the measurement of geographical displacement of crime. Using the weighted displacement quotient as part of the evaluation of the Camden initiative, researchers found a marked decrease in crime in the target area and evidence of a diffusion of benefits to the surrounding displacement buffer zone. This article examines the use of the weighted displacement quotient in the analysis of varying types of crime and seeks to address some of the methodological and statistical concerns highlighted by previous researchers. In particular, this article addresses issues of buffer area selection and evaluation. The Camden initiative serves as a case study to demonstrate the technique, as it is applied to drug, vehicle, gun, and violent crime, as well as overall crime in targeted areas of the city.