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Operation Thumbs Down: A Quasi-Experimental Evaluation of an FBI Gang Takedown in South Central Los Angeles

NCJ Number
Policing: An International Journal of Police Strategies & Management Volume: 2 Issue: 40 Dated: 2017 Pages: 442-458
Jerry H. Ratcliffe; Amber Perenzin; Evan T. Sorg
Date Published
17 pages

This article presents the findings and methodology of an evaluation of the violence-reduction effects following an FBI-led gang takedown in South Central Los Angeles.


The time series impact of the intervention was estimated with a Bayesian diffusion-regression state-space model designed to infer a causal effect of an intervention using data from a similar (non-targeted) gang area as a control. A statistically significant 22-percent reduction in violent crime was observed, a reduction that lasted at least 9 months after the interdiction. The evaluation demonstrated a minimum 9-month benefit to a gang takedown in the target area, suggesting that relatively long-term benefits from focused law enforcement activity are possible. Longer-term crime reduction beyond just the day of the intervention can aid communities struggling with high crime and rampant gang activity. Few FBI-led gang task force interventions have been studied for their crime reduction benefit at the neighborhood level. This study adds to that limited literature. It also introduces a methodology that can incorporate crime rates from a control area into the analysis, and overcome some limitations imposed by ARIMA modeling. The research method makes assumptions about the equivalency of the control area; however, statistical checks are employed to confirm the control area crime rate trended similarly to the target area prior to the intervention. (publisher abstract modified)