Body-Worn Camera RCT — Washington DC
Metropolitan Police Department / George Mason University · Washington, DC, USA · 2016
Summary
Body-worn cameras had been widely adopted based on small observational studies suggesting they reduced complaints and use of force. The DC experiment—the largest RCT ever conducted on cameras, pre-registered, published in PNAS—found null effects on every outcome measured. Cameras did not reduce use of force, citizen complaints, arrests, or assaults on officers. The finding created significant controversy because the observational literature had shown consistent positive effects. The likely explanation: body cameras change behavior when officers and citizens know they're on; in a city where cameras are ubiquitous and deployment is universal, the marginal effect disappears.
Research question
"Do body-worn cameras reduce use of force, complaints against officers, or improve other outcomes?"
Methodology
Intervention
Random assignment of officers to wear or not wear body cameras for 12 months
Assignment
Randomized controlled trial (officer)
Sample size
2,224 officers (largest body camera RCT conducted)
Primary outcome
Use of force incidents; civilian complaints; arrests; assaults on officers
Effect estimate
No significant effect on use of force, complaints, arrests, or assaults; null across all pre-registered outcomes
Decision
DC and other departments retained cameras for legal/documentation purposes; academic consensus shifted to emphasize context-dependence of camera effects
Result
Null
No significant effect on use of force, complaints, arrests, or assaults; null across all pre-registered outcomes
Evidence strength
Strong
Randomized controlled trial with large sample.
Replication status
Partially replicated
Institution
Metropolitan Police Department / George Mason University
Location
Washington, DC, USA
Year
2016
Policy area
Public Safety
Mechanism
Targeting