Greg Ridgeway, Jeffrey Grogger, Ruth Moyer, John MacDonald
Objective: Assess the effect of civil gang injunctions on crime.
Methods: Data include crimes reported to the Los Angeles Police Department from 1988 to 2014 and the timing and geography of the safety zones that the injunctions create, from the first injunction in 1993 to the 46th injunction in 2013, the most recent during our study period. Because the courts activate the injunctions at different timepoints, we can compare the affected geography before and after the imposition of the injunction contrasted with comparison areas. We conduct separate analyses examining the average short-term impact and average long-term impact. The Rampart scandal and its investigation (1998-2000) caused the interruption of three injunctions creating a natural experiment. We use a series of difference-in-difference analyses to identify the effect of gang injunctions, including various methods for addressing spatial and temporal correlation.
Results: Injunctions appear to reduce total crime by an estimated 5% in the short-term and as much as 18% in the long-term, with larger effects for assaults, 19% in the short-term and 35% in the long-term. Analyses of interrupted injunctions yielded estimates of similar magnitude and provide further support of a crime reduction effect. We found no evidence that gang injunctions are associated with displacing crime to nearby areas.
Conclusions: Injunctions represent a powerful place-based intervention strategy for police and prosecutors. Courts have recently subjected gang injunctions to closer scrutiny. Los Angeles is not litigating new injunctions and is shrinking the list of enjoined individuals. Our analysis indicates that gang injunctions appear to have contributed to crime reductions in Los Angeles and may still have an important role.
Key words: gangs, gang injunctions, difference-in-difference, spatial-temporal model