Police body-worn cameras (BWCs) can help improve transparency, accountability, and policing behaviors. This study extends prior BWC research by using a panel analysis design with a measure of treatment duration to examine how the effects of BWCs change over time. Using data from the Milwaukee Police Department (N = 1,009), we propose and test two competing hypotheses: The program maturity hypothesis suggests that BWCs will be more effective at reducing use of force and complaints over time, whereas the program fatigue hypothesis expects BWCs to be less effective the longer officers wear BWCs. We find that BWCs reduced complaints overall and that, over time, each additional month with a camera resulted in 6% fewer complaints. There was no overall relationship between BWCs and use of force, but our treatment duration model suggests that there was an immediate decrease in use of force incidents, followed by a gradual increase in subsequent months.

警察佩戴的摄像机（BWC）可以帮助提高透明度，问责制和警务行为。这项研究通过使用具有治疗持续时间的面板分析设计来扩展BWC的先前研究，以检查BWC的效果如何随时间变化。使用密尔沃基警察局（N= 1,009），我们提出并检验了两个相互竞争的假设：计划成熟度假设表明BWC会随着时间的推移在减少使用武力和减少投诉方面更加有效，而计划疲劳假设则期望BWC越长，佩戴BWC的效率就越低。我们发现BWC总体上减少了投诉，并且随着时间的推移，每增加一个月使用摄像头，投诉就会减少6％。BWC与使用武力之间没有总体关系，但是我们的治疗持续时间模型表明，使用武力的事件立即减少，随后的几个月逐渐增加。