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Public SafetyInformationNull

Police Body-Worn Cameras — Washington DC Randomized Trial

The Lab @ DC / Metropolitan Police Department · Washington, DC, USA · 2016

Summary

The Washington DC body camera trial is one of the most important null results in recent policing research. When 2,224 officers were randomly assigned to wear or not wear cameras, there was no measurable difference in use-of-force incidents, civilian complaints, or arrest patterns. The study had sufficient statistical power to detect small effects — the null result is not simply a lack of data. This finding came as a surprise: body cameras had been widely adopted under the assumption that surveillance accountability would change officer behavior. The null may reflect several things: officers may have already known cameras were possible (awareness effect was always present), body camera footage review policies were rarely enforced consistently, or the behaviors targeted were not primarily driven by lack of accountability. The lesson is not that cameras are useless — the technology may have value for post-incident review, prosecution, and evidence preservation — but that the accountability mechanism alone does not reliably change officer behavior in the way advocates predicted.

Research question

"Do police body-worn cameras reduce use of force, civilian complaints, and officer misconduct in a large urban police department?"

Methodology

Intervention

2,224 Metropolitan Police Department officers were randomly assigned to either wear body cameras or not wear them during their shifts over a period of approximately one year. Officers in the treatment condition wore cameras that recorded all police-citizen interactions (with a 30-second buffering system). The assignment was at the officer level, with officers wearing cameras during all assigned shifts. The RCT was designed and run by The Lab @ DC, a government-embedded research team.

Assignment

Randomized controlled trial at the officer level; 2,224 officers randomized (1,113 treatment, 1,111 control); outcomes measured via use-of-force reports, complaint records, and arrest data over the intervention period; Yokum, Ravishankar & Coppock analysis

Sample size

2,224 officers; approximately 200,000 police-citizen interactions during study period

Primary outcome

Use-of-force incidents per 1,000 officer hours; civilian complaints per 1,000 officer hours; arrests; judicial outcomes

Effect estimate

Use of force: no statistically significant difference between camera and no-camera officers (effect size near zero). Civilian complaints: no statistically significant difference. Arrests: no significant difference. The null findings were precisely estimated, ruling out effects larger than approximately 2 per 1,000 officer hours.

Decision

The DC null result prompted significant reassessment of the body camera policy debate; a subsequent Campbell Collaboration systematic review of 30 studies found inconsistent effects; cities that had already purchased cameras did not reverse course; the debate shifted from 'do cameras work?' to 'under what conditions might cameras work?' with attention to activation protocols, footage review policies, and community access; Congress has debated national body camera mandates regardless of the experimental evidence

Result

Null

Use of force: no statistically significant difference between camera and no-camera officers (effect size near zero). Civilian complaints: no statistically significant difference. Arrests: no significant difference. The null findings were precisely estimated, ruling out effects larger than approximately 2 per 1,000 officer hours.

Evidence strength

Strong

Randomized trial, replicated across multiple sites or studies.

Replication status

Replicated

Institution

The Lab @ DC / Metropolitan Police Department

Location

Washington, DC, USA

Year

2016

Policy area

Public Safety

Mechanism

Information

Other trials of this mechanism

Cite this entry

The Lab @ DC / Metropolitan Police Department. (2016). Police Body-Worn Cameras — Washington DC Randomized Trial. The Experiment Society Registry. Retrieved from https://www.experimentsociety.org/registry/police-body-cameras-dc-rct (primary report: https://bwc.thelab.dc.gov/TheLabDC_MPD_BWC_Working_Paper_10.20.17.pdf)

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