A simple weighted displacement difference test to evaluate place based crime interventions

Abstract

This work proposes a new statistic, the weighted displacement difference (WDD), as a simple test to evaluate crime reductions subsequent to place based interventions taking into account trends in comparison areas and potential spatial displacement or diffusion of benefits. The motivation is to have both a simple statistic that can give an estimate of the effectiveness of a crime reducing intervention, while also providing a measure of the standard error one would expect when examining crime counts simply by chance. The proposed statistic can be calculated in a spreadsheet with counts of crime before and after the intervention in both treated and displacement areas given matched control locations for each. Code to replicate the analysis as well as an Excel® spreadsheet to calculate the WDD and its standard error can be downloaded from https://www.dropbox.com/s/rg7x9bg1o3d8nsf/WDD_Analysis.zip?dl=0.