Body Worn Cameras are spreading worldwide, under the assumption that police performance, conduct, accountability, and legitimacy, in the eyes of the public, are enhanced as a result of using these devices. In addition, suspects' demeanor during police-public engagements is hypothesized to change as a result of the video-recording of the encounter. For both parties--officers and suspects--the theoretical mechanism that underpins these behavioral changes is deterrence theory, self-awareness theory, or both. Yet evidence on the efficacy of Body Worn Cameras remains largely anecdotal, with only one rigorous study, from a small force in Rialto, California, validating the hypotheses. How Body Worn Cameras affect police-public interactions in large police departments remains unknown, as does their effect on other outcomes, such as arrests. With one Denver police district serving as the treatment area and five other districts within a large metropolitan area serving as comparisons, we offer mixed findings as in the Rialto Experiment, not least in terms of effect magnitudes.
Adjusted odds-ratios suggest a significant 35% lower odds for citizens' complaints against the police use of force, but 14% greater odds for a complaint against misconduct, when Body Worn Cameras are used. No discernable effect was detected on the odds of use of force at the aggregate, compared to control conditions (OR=0.928; p>0.1). Finally, arrest rates dropped significantly, with the odds of an arrest when Body Worn Cameras not present is 18% higher than the odds under treatment conditions. The outcomes are contextualized within the framework of reactive emergency calls for service rather than proactive policing. We further discuss officers' decisions and the degree of the necessity of arrest in policing more broadly, because the burden of proof for tangible evidence necessary for making a legal arrest can be challenged with the evidence produced by Body Worn Cameras: officers become "cautious" about arresting suspects when Body Worn Cameras are present. Limitations associated with the lack of randomly assigned comparison units are discussed, as well, with practical recommendations for future research on Body Worn Cameras.
TABLE OF CONTENTS INTRODUCTION 730 I. WHAT DO WE KNOW ABOUT POLICE BODY WORN CAMERAS? 734 II. TESTING THE EFFECT OF BWCS IN LARGE POLICE DEPARTMENTS 737 III. METHODS AND DATA 738 A. Experimental Design 738 B. Settings and Procedure 738 C. Data Sources 739 D. Treatment and Comparison Geographic Sites 740 E. Apparatus 741 IV. MEASURES 742 A. Use of Force 742 B. Citizen Complaints 743 C. Arrests 745 D. Citizen-Initiated 911 Calls for Service 747 V. STATISTICAL PROCEDURE 747 VI. QUALITATIVE ANALYSES: OFFICERS' SURVEYS 748 VII. RESULTS 749 A. Descriptive Statistics 749 B. Treatment Outcomes 751 VIII. DISCUSSION AND CONCLUSIONS 754 A. Effect Of BWCs on Use of Force: Accountability and Transparency 756 B. Effect Of BWCs on Complaints: Conditional on Complaint Type 760 C. Effect of BWCs on Arrest Decisions 762 D. A Cautionary Note on Nonexperimental Designs in Future Studies on BWCs 766 CONCLUSION 767 INTRODUCTION
Police departments have begun using Body Worn Cameras (BWCs) in daily operations all over the world, in increasing rates. (1) BWCs are hypothesized to minimize the use of force in police-public encounters, reduce citizens' complaints, and increase the accountability and the legitimacy of the police. (2) At the same time, the massive growth in implementation of BWCs is not mirrored by research on their cost-effectiveness or efficiency. (3) Currently, there is a dearth of rigorous evaluation on the efficacy of BWCs (4) with much of the published work concentrating on implementation processes, (5) officers' perceptions about the use of BWCs on policing and their professional role, (6) the extent to which officers feel micromanaged in an era of digital surveillance, (7) and legal issues associated with privacy rights in the public domain. (8) One noteworthy study on the effectiveness of BWCs, in the specific area of use of force and complaints, was conducted in Rialto, California. (9) The "Rialto Experiment" showed that the likelihood that police use force when officers do not use BWCs was roughly twice that of when officers use BWCs and that the number of complaints lodged against officers dropped from 0.7 complaints per 1000 contacts to 0.07 per 1000 contacts. (10)
The Rialto Experiment was widely cited in recent cases of police use of force as a method to reduce the likelihood of these incidents. (11) The death of Eric Gardner in Staten Island, New York after police put him in a chokehold for several seconds, in contravention of the departmental prohibition; (12) the death of Michael Brown in Ferguson, Missouri, which resulted in protests in 2014; (13) and the shooting of Walter Scott by a white North Charleston police officer (14) are examples thereof. Some, including the current White House Administration, have argued that BWCs could be used as a technological advent that would revitalize police-public relations and prevent these incidents. (15) Had the officers involved in the incidents cited above been issued BWCs, they may have dealt with these situations differently. The Rialto Experiment was suggested as the necessary evidence to support this contention, including a citation by the United States district judge in the 2013 ruling against the New York Police Department (NYPD) over stop and search. (16) The Rialto Experiment has influenced policy discussions over improvements in police conduct and legitimacy, including the recent discussion by the President's Task Force on 21st Century Policing. (17)
Yet the Rialto Experiment is only one study; replications are urgently required in order to show whether these findings represent an anomaly attributed to the Rialto context, to the novelty of these devices in police operations, or both. (18) Perhaps as important, Rialto is a small department, with about 50 frontline officers force-wide. (19) It remains unknown whether similar effects on police-public encounters would be detected--in both directionality as well as magnitude--in large police departments, within large metropolitan settings.
In the present study, we tested the effect of using BWCs in police frontline operations on police use of force, complaints lodged against officers and arrest, in one of the largest state and local law enforcement agencies in the United States--the Denver Police Department--over a period of six months. One police district out of six was assigned BWCs, while all other districts served as comparison sites without BWCs. We observed the effect of BWCs on these outcomes based on adjusted odds ratios at the aggregated level: comparing the odds of use of force, complaints, and arrest in the 'treatment district' compared to five other districts, as a way to estimate the effect of using BWCs.
After reviewing the existing research on BWCs and examining the theoretical mechanisms that underpin the effect of these devices on police--public encounters, we next lay out the Denver Police Department experiment and its design. The outcomes of the study are then presented, broken down into different outcomes of interest. The practical implications, with an emphasis on avenues for future research, are contemplated in the discussion chapter, including the methodological limitations of the present study.
WHAT DO WE KNOW ABOUT POLICE BODY WORN CAMERAS?
Ariel, Farrar, and Sutherland have recently reported the findings of what is now commonly referred to as the Rialto Experiment. (20) The study, conducted in the small jurisdiction of Rialto, California, with just over fifty frontline officers, compared nearly 500 police shifts in which all police-public encounters were assigned to treatment conditions and an equal number of police shifts to control conditions. (21) During treatment shifts, officers were asked to videotape all their encounters with members of the public, to announce to the parties with whom they have engaged that the encounter was videotaped, and to subsequently store evidence on a secured cloud. (22) In control shifts, the officers were tasked never to use the devices. (23) Outcomes were then measured in terms of officially-recorded use of force incidents and complaints lodged against Rialto police officers. (24) Following this twelve month experiment, Ariel, Farrar, and Sutherland reported a relative reduction of roughly 50% in the total number of incidents of use of force compared to control conditions and a 90% reduction in citizens' complaints, compared to the twelve months prior to the experiment. (25)
The findings have generated heated debates worldwide, particularly around the transferability of the findings to other jurisdictions, or to larger police departments. (26) Whether unique circumstances in Rialto jeopardized the external validity of the test were also raised. (27) Major metropolitan cities, and with them large law enforcement agencies, operate on a different scale to small or even medium sized forces. (28) Larger forces can be exposed to more diverse problems, including a nighttime economy of a different scale than small-scale departments, an incomparable volume of calls for service, and potentially more serious crimes than local agencies. (29) Training, interagency collaborative work and, perhaps, the expertise of officers and how likely they are to use force are potentially different in large versus small police departments, not to mention police cultures, promotional processes, and budgets. (30)
Despite these discussions, additional research on BWCs is virtually nonexistent. The most updated literature review when this study was conducted has concluded that:
Independent research on body-worn camera technology is urgently needed. Most of the claims made by advocates and critics of the technology remain untested.... Researchers should examine all aspects of the...