Street Gangs, Gun Violence, and Focused Deterrence: Comparing Place-based and Group-based Evaluation Methods to Estimate Direct and Spillover Deterrent Effects

Objectives: Focused deterrence seeks to change the violent behavior of gangs not directly targeted by the intervention by leveraging network ties between groups. This study appraises group-based and place-based methodologies in detecting direct and spillover crime reduction impacts of a focused deterrence strategy implemented in Oakland, California. Method: Quasi-experimental designs and panel regression models were used to compare shooting trends for directly treated gangs and census block groups to shooting trends for comparison gangs and block groups that did not directly receive the treatment. The design further analyzed whether vicariously treated gangs and untreated block groups immediately surrounding treated block groups experienced spillover shooting reductions. Results: The focused deterrence program generated statistically significant direct reductions in shootings in treated block group areas and by treated gangs relative to shootings in untreated block group areas and by untreated gangs, respectively. Spillover deterrent effects of varying magnitudes were found when shooting trends by vicariously treated gangs and in surrounding block groups were compared to shootings trends in comparison units. Conclusions: Group-based evaluation methodologies were better positioned to detect changes in violent gang behaviors after treatment and to shed light on deterrence mechanisms supporting program efficacy. Future focused deterrence studies should be theory driven rather than black box evaluations.