Objectives

This study assesses the effects of body-worn cameras (BWCs) on rates of fatalities arising from police-citizen encounters. While existing experimental research has not examined this outcome because it is so rare, the staggered roll-out of BWCs across the nation’s law enforcement agencies provides an opportunity for quasi-experimental analysis.

Methods

Difference-in-difference (DID) analyses using Poisson models compare changes in U.S. law enforcement agencies’ fatality counts with changes in BWC acquisition. Using a federal law enforcement survey focused on body worn cameras (LEMAS-BWCS) and media-sourced data on fatal encounters from fatalencounters.org (FE), the research examines agencies acquiring BWCs between 2013/14 and 2015/16 and those that did not acquire them up to 2016 and had no plans to do so. It includes a fixed effects annual panel data analysis with data from 2005/06 to 2018/19 and two two-group analyses focusing on a pre-treatment period (2010/11 to 2012/13) and a post-treatment period (2016/17 to 2018/19). The latter includes a propensity score matched comparison.

Results

Two out of three DID analyses showed statistically significant negative effects of BWCs on citizen fatalities. The propensity score matched two-group analysis returned a non-significant negative effect.

Conclusions

The research finds some evidence for BWC effects on citizen fatalities. However, there are important validity threats to this conclusion. These include the possibility that BWC acquisition serves as a marker for other policy changes focused on BWC-acquiring agencies in the 2013/14 to 2015/16 period and beyond.

中文翻译：

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警察佩戴的摄像头能减少公民死亡吗？一次全国性自然实验的结果

目标

这项研究评估了随身摄像机（BWC）对因警察与公民相遇而导致的死亡人数的影响。尽管现有的实验研究由于这种结果非常罕见而没有检查到这一结果，但在全国的执法机构中交错部署《生物武器公约》为准实验分析提供了机会。

方法

使用Poisson模型进行的差异（DID）分析将美国执法机构的死亡人数变化与BWC购置变化进行了比较。该研究使用联邦执法机构针对穿戴式摄像机（LEMAS-BWCS）进行的调查，以及通过媒体获取的来自fatalencounters.org（FE）的致命事故数据，该研究调查了2013/14年至2015/16年间购买BWC的机构以及直到2016年都没有收购他们，也没有计划这样做。它包括固定效应年度面板数据分析（包含2005/06至2018/19的数据）和两个两组分析，重点是治疗前期（2010/11至2012/13）和治疗后期（2016/2015）。 17至2018/19）。后者包括倾向得分匹配比较。

结果

DID分析中有三分之二显示出BWC对公民死亡的统计显着负面影响。倾向得分匹配的两组分析返回了非显着的负面影响。

结论

该研究发现了一些证据表明，《生物武器公约》对公民的死亡具有影响。但是，该结论存在重要的有效性威胁。其中包括在2013/14至2015/16期间及之后，收购BWC可能会成为其他针对以BWC收购机构为重点的政策变化的标志。