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Assessing the gang-level and community-level effects of the Philadelphia Focused Deterrence strategy

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Abstract

Objectives

Violence reduction initiatives based on focused deterrence strategies have gained attention in recent years due to their empirical support. The evaluations have generally assessed the impact of this intervention on trends in gun violence at the aggregate level, but not at the gang level. The current study evaluates both the community- and gang-level impacts of the Philadelphia Focused Deterrence strategy.

Methods

The intervention was assessed using a quasi-experimental design that measured trends in shootings over a twelve-year period, including two years after the implementation of the initiative. Propensity scoring and matching techniques were used to match neighborhoods and gangs, and a number of regression models were run to assess impact.

Results

Although a statistically significant reduction in total shootings across the treated neighborhoods was observed when compared to matched neighborhoods, the findings at the gang level were mixed. Models comparing shootings around gang territories showed significant reductions when compared to shootings around the territories of matched gangs, but pre-post-only models of treated gangs using the more rigorous measure of gang-involved shootings did not show evidence of impact.

Conclusions

The findings suggest that focused deterrence may provide a mechanism for general deterrence among a broad pool of potential offenders. Specifically, violent gangs, even when targeted, may not be affected similarly for a variety of reasons. To better understand who is receiving the deterrence message and responding to it, future evaluations of focused deterrence strategies, when assessing impact, should include measures of the dosage of the message and other components relative to individuals and their groups.

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Notes

  1. A study published after the more recent meta-analysis sought to specifically examine the importance of the notification meetings. Hamilton et al. (2017) completed a randomized control study in which probationers and parolees were randomly assigned to attend a call-in meeting, or not. Individuals who attended the call-in meeting were less likely to be arrested in a 17-month follow-up period than individuals in the control group and individuals who were asked to attend the call-in, but did not. These results were not significantly affected by self-selection to attend the meeting (for those in the treatment group). The authors concluded that deterrence is clearly a mechanism at work via the message delivered in the call-in meetings.

  2. Over the evaluation period, some gangs split into subgroups; for the purposes of the impact analyses, the subgroups were not counted as new groups.

  3. “Activity” of gangs captured a variety of characteristics that included violence-activity level (hot, warm, or cold) and other activity characteristics related to type of activity and specialization. The PPD had clear definitions for determining the violence-activity level. At each of the audit meanings, the research team would review the definition before validating the activity level. The audits also reviewed the gang classifications (street gang, corner drug sales, drug-trafficking organization), but it is important to note that, across the audits, none of gangs change with regard to its classification.

  4. The matching routine started with 16 treatment gangs but 2 of the treated gangs were dropped because they were off the common support. It is likely these gangs were difficult to match because their gang territories were on the low end of concentrated disadvantage, but had high numbers of probationers. One of the two gangs’ territories was located in an area that was not heavily populated with residents who identified as Black. The overwhelming majority of gangs/groups in Philadelphia are comprised of members who are Black and/or based in neighborhoods made up mostly of Blacks.

  5. While the Mahalanobis matching made the treatment and comparison gangs more similar than the unmatched gangs, we computed the gamma statistics and Rosenbaum bounds (2002) to assess the effects of unobserved but relevant endogenous predictors of selection into treatment. Our findings for significant focused deterrence effects are more robust for the half-mile buffer shootings outcome than the quarter-mile buffer shootings outcome. For the quarter-mile buffer model, the analysis suggests that an unobserved variable that increases the odds of selection into treatment by as low as 5% might question our significant findings (at a 5% significance level). A gamma level of 1.05 might increase our p values to above the 0.05 level and the treatment effect might reduce to − 1.438. However, the unobserved predictor would need to increase the odds of selection into treatment by about 25% before it caused us to question our significant findings at the 10% confidence level (gamma = 0.125 before the p-critical crosses the 0.1 threshold). The equivalent treatment effect would have to be reduced to − 1.063 for that to happen. The findings are somewhat more robust for the half-mile buffer outcome. The gamma level at which the p value crosses the 0.05 significance level is 1.5, suggesting that the unobserved but relevant predictor would need to increase the odds of selection into treatment by 50% before we questioned our findings at the 5% confidence level. The treatment effect would drop to − 3.063. The unobserved predictor would need to double the odds of selection into treatment (gamma = 2.0) before we questioned our finding at the 10% significance level (for a bias equivalent effect of − 2.563). These data are available upon request.

  6. https://www.campbellcollaboration.org/escalc/html/EffectSizeCalculator-SMD24.php

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Acknowledgments

This research was supported by grant number 2013-IJ-CX-0056 awarded by the U.S. Department of Justice, National Institute of Justice. Opinions or points of view expressed are those of the authors and do not necessarily reflect the official position or policies of the U.S. Department of Justice. We thank all of our law enforcement partners for their willingness to share data, with special thanks to the South Gang Task Force, PPD’s Central Intelligence Unit, PPD Research & Analysis Unit, and the DAO. We are also grateful for the research support provided by Hannah J. Klein, Lauren Mayes, Justin Medina, and Matt Stephenson.

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Correspondence to Caterina G. Roman.

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Roman, C.G., Link, N.W., Hyatt, J.M. et al. Assessing the gang-level and community-level effects of the Philadelphia Focused Deterrence strategy. J Exp Criminol 15, 499–527 (2019). https://doi.org/10.1007/s11292-018-9333-7

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