The Effect of Police Body Cameras

The first randomized controlled trial of police body cameras shows that cameras sharply reduce the use of force by police and the number of citizen complaints.

We conducted a randomized controlled trial, where nearly 1,000 officer shifts were randomized
over a 12-month period to treatment and control conditions. During ‘‘treatment shifts’’
officers were required to wear and use body-worn-cameras when interacting with members
of the public, while during ‘‘control shifts’’ officers were instructed not to carry or use the
devices in any way. We observed the number of complaints, incidents of use-of-force, and
the number of contacts between police officers and the public, in the years and months
preceding the trial (in order to establish a baseline) and during the 12 months of the
experiment.

The results were that police use of force reports halved on shifts when police wore cameras. In addition, the use of force during the entire treatment period (on shifts both using and not using cameras) was about half the rate as during pre-treatment periods. In other words, the camera wearing shifts appear to have caused police to change their behavior on all shifts in a way that reduced the use of force. A treatment that bleeds over to the control group is bad for experimental design but suggests that the effect was powerful in changing the norms of interaction. (By the way, the authors say that they can’t be certain whether the cameras primarily influenced the police or the citizens but the fact that the effect occurred even on non-camera shifts suggests that the effect is primarily driven by police behavior since the citizens would not have been particularly aware of the experiment, especially as there would have been relatively few repeat interactions for citizens.)

It is possible that the police shaded their reports down during the treatment period but complaints by citizens also fell dramatically during the treatment period from about 25-50 per year to just 3 per year.

Here’s a graph of use of force reports before and during the treatment period.

Police cameras will have some negative effects. When a police officer is accused of something will lawyers have the right to subpoena years of camera footage looking for anything problematic? Think about the OJ case. Perhaps tape should be erased after one year.

Nevertheless, the results of the study are impressive. More generally, I worry that there is no solution to the problem of government mass surveillance but at the very least we can turn the cameras around and even the playing field.