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RESEARCH ARTICLE: A randomized control trial evaluating the effects of police body-worn cameras

David Yokum, Anita Ravishankar, and  View ORCID ProfileAlexander Coppock

PNAS May 21, 2019 116 (21) 10329-10332; first published May 7, 2019

  1. Edited by Susan A. Murphy, Harvard University, Cambridge, MA, and approved March 21, 2019 (received for review August 28, 2018)

"Police departments are adopting body-worn cameras in hopes of improving civilian–police interactions. In a large-scale field experiment (2,224 officers of the Metropolitan Police Department in Washington, DC), we randomly assigned officers to receive cameras or not. We tracked subsequent police behavior for a minimum of 7 mo using administrative data. Our results indicate that cameras did not meaningfully affect police behavior on a range of outcomes, including complaints and use of force. We conclude that the effects of cameras are likely smaller than many have hoped."


"Police body-worn cameras (BWCs) have been widely promoted as a technological mechanism to improve policing and the perceived legitimacy of police and legal institutions, yet evidence of their effectiveness is limited. To estimate the effects of BWCs, we conducted a randomized controlled trial involving 2,224 Metropolitan Police Department officers in Washington, DC. Here we show that BWCs have very small and statistically insignificant effects on police use of force and civilian complaints, as well as other policing activities and judicial outcomes. These results suggest we should recalibrate our expectations of BWCs’ ability to induce large-scale behavioral changes in policing, particularly in contexts similar to Washington, DC."

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