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

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.


One of the negative consequences of police cameras might be a higher incidence of

Police selfies.

A dystopian scenario if there ever was one.

Contortionist cops taking selfies? Worth it, I guess.

Better than extortionist cops taking bribes

If police hesitate to use force, is that an unadulterated good thing? Do incidents of bodily injury increase for police or citizen non-perpetrators, for example, in domestic violence situations? If incidents do not increase, then keep the cameras rolling.

In the current environment, yes, police should be hesitating from using force more than they are now.

I could see them becoming too reluctant. We'll see if we ever get there.

What's your basis for that statement?

Our ridiculously high rate of police violence, I'd assume.

see today's NY Times article:
"Despite Scrutiny, Police Chokeholds Persist in New York City"

and that's in a modern, well trained and well supervised city police force; things get much worse in smaller cities, towns and counties. the US prison population is shockingly high by world standards-- that's a clear indicator of an out control police state

I don't know if our police violence rate is high or not, having not seen any metric to make that judgement. The question is whether violence is being used appropriately. After all, criminals need to be stopped, and sometimes that requires violence.

All of the recent controversies seem justified to me. Michael Brown was a violent thug who assaulted a police officer who defended himself. Garner was a lifelong criminal out on parole, breaking the law, and resisting arrest (he also wasn't killed by the chokehold, but by cardiac arrest during the ambulance ride owing to his poor health and the stress of the incident).

Rodney King was a drugged out criminal who led police on a high speed chase while under the influence.

Somehow its almost never law abiding people who don't resist arrest that end up in these situations. All of this outrage seems like monday morning quarterbacking from a bunch of dudes that know nothing about the underclass and probably have never been in a real fight.

I got interested in a local police shooting of an 18-year-old violist. I ran into the dead teen's mom a week later at the site of the shooting and urged her to sue the DEA. Three years later the family was awarded $3 million by a judge.

But that case got very little publicity until the award was made.

@asdf See this article:

@asdf -- you only hear about the fatal uses of force. This study tracked all uses of force. You do see plenty of instances of cops tasering people and dragging them out of their cars over simple speeding tickets, and that's a problem -- and those are instances where the cops do know that the dashcam is running. This study would suggest that they use even more force when they know that the only testimony will be them, other cops, and the alleged "resisting" criminal.

I believe the preprint (which came out a year or two ago) showed no increase in crime.

The problem with policing in domestic violence situations is not that cops hesitate to use force, it is that when they arrive the fighting is over and they often do nothing, as the couple declines to press charges and falls back into their standard patterns of abuse. (or, from some perspectives, this is fine and cops are to aggressive in arresting someone involved in couples quarreling). In no situations is the need for the police to show up and just start beating someone extra judicially. Even if the beat an abuser, illegality aside, there are good chances the abuser will take it out on the victim later.
Cop violence is generally abuse of authority (often for the crime of 'disrespect of police officer'). Not to preserve law and order, but to punish a lack of obsequiousness to the cop.
I'm curious to know what 'crimes' are prevented by allowing cops to beat citizens in their custody.

There would be only two reasons to think that hesitation to use force was bad -- if it led to more police injuries, or if someone just likes the idea of the police beating people. If there was an increase in police injuries during this time, you would certainly have heard about it from the cops, if not the researchers. That would put us into the "unadulterated good thing" territory.

I won't address the second reason.

Under what circumstances is it in the public interest for cops to use less force? Cops sitting in diners eating doughnuts are in no danger of being the subject of complaints about 'police brutality'. There are, of course, some costs for the rest of us (not borne, of course, by residents of Fairfax County, Va.).

Highway patrols seem to be using cameras for a long time and that does not cause police officers to eat donuts all day. Airports are full of cameras and anyway TSA people keep getting their shoes off.

Force is not equal to deterrence or good results.

Highway patrol are tax collectors; TSA is a make work program. Not very good examples.

Fewer complaints is a far better metric than less use of force.

The police deal with the world's troublesome people. What they complain about might not be what an ordinary person would complain about.

This may come as news to you, but in the civilized parts of the world the police seem to be able to do their jobs without randomly shooting people (and their pets).

They also don't regularly deal with heavily armed criminals so your comparison is dumb.

I don't even like dogs, but any tour through the many stories of police killing dogs on sight (even dogs in cages) ought to make you wonder what's going on.

Many people own dogs for protection as well as companionship. It is reasonable for police to believe that when a dog sees its owner being attacked, the dog will act to protect its owner. Testable hypothesis: are large dogs shot more frequently than small dogs?

Dan, you don't understand. American dogs aren't like European dogs. The breeds are different; there is a culture of dog violence; and most importantly, due to easy access, a lot more American dogs own and carry firearms.

A really convoluted way to say the US is not a civilized part of the world.

A really convoluted way not to call attention to the reality of the urban slums in this country.

Heavily armed assault terriers.

Which certainly explains the lack of guns in the hands of most of the controverial cases that most people concerned with the current police culture and tatics point to...

Erick and crew: "Guns are scary, Guns are scary!"

20 years later

Police Officer: "Suspect had a weapon, I was scared for my life"

Give us the numbers or shut up.

It is in the public interest for cops to use less force in ALL instances possible. This is basic Peelian principles -- every use of force lowers respect for the police, lessing the consent of the governed, and makes ALL policing more difficult. That means that force should only be used when all efforts are persuasion have failed, and then the absolute minimum force required to effect the arrest.

If you can lead them along by the elbow, even if they have "resisted" and the policy says that you are authorized to twist their arm behind their back, you still lead them by the elbow, because that is the least amount of force necessary.

I recall that policemen with college educations also use force less often than those with less education.* It'd be interesting to know how the effect of cameras varies with education, experience, ethnicities of officer and civilian, etc.

(*Is education only a proxy for verbal aptitude or, worse yet, general intelligence?)

I would guess that this is more of a correlation than causation. The cops who are college graduates probably didn't enter the field just to abuse their power. The ones who didn't are are just 40 year old high-school bullies are more apt to.

Interesting questions. You would also have to take into account the difference in career paths for policemen with tertiary education.

This statement has "confounding variable" written all over it.

I wonder what the effect will be on written police reports, which are shockingly inaccurate and biased. By the way, I'd argue there was anecdotal evidence provided for this 25 years ago with the debut of Cops on Fox. One of the many criticisms of the show is that the cops only act like that on camera. Apparently, they do.

I am consistently amazed that anyone treats written police reports as reliable sources of information.

+1 Maybe someone can make a real life drama from a combination of police reports and video.

Who gets the IP rights to the materials.

Here's a 2005 study of police cruiser dashboard cameras:


You missed the point of Ferguson really badly.

We have had video of Michael Brown launching his crime spree by attacking the little Asian shop clerk since August 15th. The media and the Obama Administration studiously ignored it.

As Hayek quoted Lenin, Ferguson was about Who? Whom?

The media ignored it? Then, how exactly did you hear about it? We're you there to personally witness it?

When Steve Sailer says that "the media studiously ignored it," what he means is that the media covered it, but that some people did not come to the conclusions that he wants them to. Lots of people did come to those conclusions, of course. Heck, there was even a fake Michael Brown video making the rounds on conservative and social media. Apparently that is not enough.

I've found it to be an iron law of the internet that whenever someone says "nobody wants to talk about X," if you Google X, you will find lots of people talking about X. Likewise, most of Steve Sailer's world views are only interesting so long as he can imply that there is something forbidden or otherwise suppressed about those views.

Or, more logically, he means they reported it, then completely ignored it in any of their reasoning afterward.

Or people incorporated it into their reasoning, but just came to a different decision.

If decision means "I really really really don't like it..." then Yes.

Does anyone know how video evidence collected by police applies in court.
If you make a statement to police, they can use it against you in court.
If you try and use a statement made to police in your favor it will be objected to and called hearsay.
So if police capture evidence that contradicts the case will it be used to aid defendants or only used to prosecute them?

If the evidence is exculpatory, they have to turn it over to the defense. See Brady v Maryland.

Some states (I specifically know about Texas and the Michael Morton Act) even removed the exculpatory condition, and require that all evidence be turned over the defense en masse.

Brown's status as a criminal does not mean that the officer used an appropriate amount of force. Surely there is a way for a police officer to disable an unarmed criminal, even a violent one, without multiple gunshots to their center of mass.

Agree. But the narrative being presented was misleading. The narrative depicts a young man wearing a graduation cap and gown, going about his ordinary business, not harming anyone, who is then ruthlessly gunned down by a police officer just for sport.

the media narrative came about because of the other eye witnesses who first spoke to the media, while the police were silent. The police eventually got around to trying to unwind that narrative, but the idea of 'hands up, don't shoot' had already spread.

Yeah, you should totally tell us your opinion of how to handle violent thugs who attack you in detail.

Brown's status as a criminal is important because

1) When the officer is considering whether the suspect is likely to be dangerous that's an important variable that shifts the probable outcomes of his decisions
2) To the extent its not 100% clear what happened the character of those involved informs that likely probabilities of what happened

In the case of Micheal Brown the officer *could* have put his car in reverse and not needed to worry about getting hit any more. He didn't need to pull his side arm -- and that tatic would have also gone a long way to preventing Brown from being able to grab onto the pistol.

"Brown’s status as a criminal is important because..."

This is a funny phrase, but typical. In contemporary America, government overreach has made us all criminals. Which is convenient for agents of the state, because then they get to selectively decide who to punish and how.

We could compare Michael Brown's "status as a criminal" to Julia Shield's status as a white woman, driving around in body armor randomly shooting at people. Funny that the police found a way to get her in custody without incident or injury.

"*could* have put his car in reverse"

Dereliction of duty? Brown was not jaywalking, he was wondering down the middle of the road blocking traffic.

He lucky some motorist didn't just get pissed off and run him over, like what should have happened to the equally asinine protesters doing the same.

"Surely there is a way for a police officer to disable an unarmed criminal, even a violent one, without multiple gunshots to their center of mass."

In old cowboy movies, the good guy would shoot the bad guy in the hand. Maybe the police should be trained to do that.

Only someone with NO firearms experience would make that statement.

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.

Police worn cameras film the public, not the police, from the wearers POV, so it is not turning "the cameras around". That is why bystander video is important in excessive force complaints.

Winston Smith's TV watched him.

Yes, but I thought that was one of the main advantages of police worn video cameras.

I mean, if a cop says John Doe had a gun but the video clearly shows John Doe with empty hands, then the justice system has some useful evidence which can be used to push back against police testimony.

Or if the cops lose a bust, the cops can go back to the videotape and maybe see somebody else in the car doing something illegal like drinking, so they go arrest that witness and get him to roll over on the guy they really want.

As others point out, the study would be better if it also included some other statistics related to crime and particularly violent crimes in the area.

That said, I do think it's generally a good thing when violence in police interactions with the public is kept to the lowest level possible. (Even some who just robbed a store using physical intimidation should not be shoot if avoidable -- the crime does not support the death penality.) Moreover, the problem of police violence and choice to escalate rather than defuse is a serious trend that needs to be reverse.
From today's AP News wire:

True, but someone rushing a cop and trying to take his gun away from him does deserve to be shot. I have no issue with that at all.

Only if you know that is what really happened. Also, it would be nice to know how the cop came to be in that situation in the first place. Perhaps how the police approach a situation makes a difference, getting so close by default and thereby making deadly force the only option if things go out of control. Sure looked that way in the Tamir Rice shooting.

And we do know that's what really happened.

Really? No question about it?

Several witnesses testified this to a grand jury and forensic evidence backs it up.

There is no such thing as a reliable witness. That's what the cameras are for.

When there are several people with the same story and it's backed up by the forensic evidence, there's a good shot that it is true.

I don't think anyone saying police don't have any right to use deadly force or protect themselves. If you're referring to the Michael Brown case I think that's very complicated and even if one thinks Wilson should not be charged with a killing (accidental, manslaughter or murder) I believe that was a situation where it didn't need to get to the point someone died. There were a lot of choices that played out on both sides. However, the police are supposed to be proffessional and I think the situation could have been controlled and Brown taken into custody without any shots being fired. The first step for that outcome, though, was that Wilson would have needed to back off, stay a safe distance if he's not physically equal to Brown and let backup assist. Keep in mind, at this point the only thing Brown had done that WIlson know about was walking down the middle of the steet in his own neighborhood -- I see people doing that all the time where I live.

You see people walking down the middle of a street, blocking traffic? And nobody does anything?

Where the hell do you live? How is this complicated? You try to wrestle a cop's gun from him you are going to get shot. Contra DeBlasio, this goes for white folks as well as black.

What's interesting is society's changed views towards police force. Up until the early 1970s, a policeman in Detroit (and this was true elsewhere) could shoot at a fleeing felon. Which means a guy that stole a car or even a TV could be shot in the back while escaping with the loot. Times have changed. Here in the Philippines, I don't see much crime except pickpocketing (had it happen to me in a crowded subway) and petty theft. And they are well armed, but polite. I don't think however it's the guns, it's more the culture, but I can't prove it.

New systems bring about new problems.
The NFL is proof that video cannot aid human beings in reaching conclusions.

Ok, explain to a non-football fan how the NFL is proof of that.

He's a cowboys fan upset that the video allowed the refs to correctly fix their call based on the rules, I'd guess

Yes this is true.
They shot themselves in the foot and never should have let the game come down to that.
So I am not really sympathetic.

The use of reply in the NFL has not brought clarity to calls challenged on the field, nor has it improved accuracy in the interpretation of the rules during the game. Officials still make errant calls. The review footage has created more frustration as referees continue make errors when what appears to be obvious evidence is present.

My point is that video does not remove the human factor, people are still going to analyze and form opinions from video, video is not factual information.

There is a pretty big difference between using a video to show what happened during a criminal confrontation and using one to determine how to interpret a 800 word rule about what constitutes a catch in a game. Also pretty ironic for a Cowboys fan to be upset about the officiating in a game...

I can provide you the anecdotal evidence of the man who died in Staten Island from a choke hold caught on video. Did everyone see the video as fact of 'murder' or the fact of a cop 'doing his job?'

It seemed to be that people took sides and formed opinions even though it was caught on tape.

Remove the subject matter, what I am trying to get it as on body video is not a solution to problems police nor citizens face when altercations go awry.

NFL replay has probably reduced bad calls by 80%. But since the number is not 100%, you call it proof that it doesn't provide "aid." It does not bring "clarity."

Lord. Might as well say that since we can't 100% seal the border, it might as well be fully open.

Get in line with Alex.

Might as well say that since we can’t 100% seal the border, it might as well be fully open.

Indeed, I've seen people make that basic statement. You'd hope never to see it on a site called "Marginal Revolution," but it happens (not regarding illegal immigration, AFAIK).

I've heard two explanations for the drop in comments paints. The first is that the camera wearing police are deterred from abusing their authority. The second is that members of the public are less likely to make false complaints.

If the public believe the former and police the latter there might be wide support for cameras.

There's one thing you will never hear a cop say about body cameras, and that's "nothing to hide; nothing to fear."

I would strongly agree with a fairly short period of retaining footage. If there was a systematic issue that came to the fore in a specific incident, then one year would be plenty. If it was something crazy that happened in the heat of the moment, then one year should be plenty to find that the specific officer was not generally abusive of the authority vested in him by the state.

Among other things, acceptable behaviours in one period may be unacceptable in another. For example, no one used to be particularly bothered if some cops kicked some hooligan hard enough to fill his pants with poop, but these days we consider that to be abuse of authority. In those days, we regarded a punch-up as not that big of a deal, and I'm inclined to agree, when compared to the violence one can inflict upon a mind, but which does not leave the physical evidence of scars, etc. to accompany it.

An ordinary person's record with law enforcement is never deleted.

Fair point. But one's record does not track every move, only the formally recorded and "proven" mistakes/errors.

When I was young, police would look into parked car windows where young persons were engaging in various types of foreplay. If police are now wearing cameras, and look into windows with the camera on, where can I get the video.

You are not the real Bill. The real Bill always writes in modern American haiku.

I am the real Bill.

I'm goin stream of consciousness....

Child pornography charges, coming up!

>Perhaps tape should be erased after one year.

That's one of the very dumbest things I've ever heard. Lawyers might ask for old tapes, so we should erase them, so they can't possibly have them? How about courts do their jobs instead? Too much to ask?

Cops will not fight body cameras. I am sure that many want them. However, their union will demand a raise in exchange for the "burden" of wearing them. Because that is what unions are for.

"A treatment that bleeds over to the control group is bad for experimental design but suggests that the effect was powerful" - not really - it suggests that this is a

After thinking about for awhile, since all the officers know they are part of a study (whether wearing a camera or not), I feel like they all would have some incentive to change their behavior. The results seem to show that. That would also mean the results imply that roughly half of the cases of an officer using force and roughly 90% the citizen complaints about officers are due to the officers behavior.

Seems like more action on citizen complaints would be a cheaper first step to changing officer behavior.

Very interesting data! Another interesting piece from the Daily Mail:
'Police officers wearing body cameras are 50% less likely to use force and 90% less likely to have complaints made against them, new study reveals'

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.

Because we lack the technology to digitally store many hours of digital video? Hmmmm. If the incident in question is on video, the video of that incident will likely go a long way of showing us who was right or wrong (ok maybe that's too optimistic, it will at least force both sides to limit the degree their narrative can drift from the objective record).

I think having years worth of archive footage could provide a lot of useful raw data that could be great for studies, evaluations and for historians. If some lawyer really is willing to subpoena 100,000 hours of footage and pay his staff to watch it all trying to find patterns then let him do it.

this is a good thing and protects good cops too from false rape accusations and other stuff. so it hurts bad cops and protects good cops. win-win, quickly implement it

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