A quasi-experimental synthetic control evaluation of a place-based police-directed patrol intervention on violent crime

Abstract

This research evaluates the impact of an implementation of a place-based police-directed patrol intervention—originally based on the Data Driven Approaches to Crime and Traffic Safety (DDACTS) model—on violent crime in Flint, Michigan, USA. We utilize recent advances in synthetic control methods to implement a retrospective quasi-experimental design across seven separate intervention areas, producing a counterfactual estimate of what would have happened to violent crime had the intervention never been implemented. We use survey weight calibration to produce counterfactual intervention areas using comparison block groups in Flint, and account for treatment diffusion by using comparison block groups from Detroit. The synthetic control method calibrated a set of weights to exactly match the intervention hot spots to counterfactuals from Flint and Detroit. Although basic trend analyses suggested declines in violent crime in the treatment areas, the synthetic controls raised questions about treatment effects. Specifically, the Flint comparison revealed an unexpected increase in aggravated assaults associated with the intervention, whereas the Detroit comparison suggested a similar effect but also possible reduction in robberies. This evaluation presents mixed findings regarding the effect of the intervention on violent crime. Inconsistent program effects may be attributable to incongruences between the program as implemented and the prescribed DDACTS model on which it was based. The findings also suggest the need for future research to investigate potential differential effects of directed patrol on specific types of violent crime. The synthetic control method provides a powerful means for counterfactual estimation in retrospective evaluations.