The evidence behind body worn cameras

On Monday, the Metropolitan Police Service announced that it would be adopting body-worn cameras across most of the force. The roll-out is believed to be the largest-scale use of such cameras in the world. In total, about 22,000 front-line police officers in London will be equipped with them, to record their interactions with civilians. It is hypothesised that cameras both reduce the number of complaints against police officers and reduce the use of force by officers.

Complaints against police

A number of studies have examined whether body-worn cameras affect the quantity of complaints made against police officers. In September this year, researchers from the University of Cambridge published a report which showed that complaints by members of the public against police officers fell by 93% over 12 months following the introduction of cameras. The research involved police from Northern Ireland, the West Midlands, West Yorkshire, and Cambridgeshire, as well as the Rialto and Ventura police departments in California. The findings showed there were 113 complaints made against officers during the year trial period, compared with 1,539 in the 12 months before. Interestingly, there was no statistically significant difference between the number of complaints received by officers wearing cameras and those who did not wear them. The researchers attributed this finding to “contagious accountability” whereby police officers adopted better practice across the force due to the introduction of cameras.   

The study confirms a number of previous findings. In 2015, a study in the Journal of Quantitative Criminology found that the  number of complaints filed against police officers in America dropped from 0.7 complaints per 1,000 contacts to 0.07 per 1,000 contacts when body worn cameras were introduced. Similarly a study in Orlando found that body-worn cameras were effective in reducing serious external complaints by 65%.

Researchers have typically hypothesised that body-worn cameras reduce complaints against police by making both officers and civilians consider their actions more carefully. In addition, their use  thought to dissuade frivolous external complaints, since a complete record of the encounter exists.

The use of force

In addition to reducing complaints, a number of studies have examined whether body-worn cameras reduce the use of force by police officers. A randomized controlled study in America found that officers not wearing cameras were twice as likely to use force as those wearing them. However, a separate study which examined police forces is multiple countries found that body-worn cameras did not reduce the use of force by police officers. In addition, the study found that cameras led to an increase in violence against police officers.

In contrast, a study from the UK found that body-worn cameras did reduce the likelihood of police officers using force and the likelihood of a civilians using violence. However, there was an important caveat: The cameras had to be in use for the entire encounter. If a camera was turned on during the encounter it had the potential to escalate the incident and increase the likelihood of force or violence.

Some evidence suggests that body-worn cameras may increase the use of the most serious force. A study in America found that police officers wearing body cameras was associated with a 3.64% increase in shooting deaths of civilians. The researchers attribute this increase to officers being more confident in administering lethal force due to the proof of wrongdoing which cameras provide. Incidents of police officers shooting civilians in the UK are extremely rare. However, the Metropolitan Police Service has been involved in a number of high profile incidents. This research suggests that the introduction of body-worn cameras could lead to a small increase in such incidents.


So whilst body-worn cameras appear to be effective in reducing the number of complaints made against police officers, t evidence of their effectiveness in reducing the use of force by police officers is less conclusive. Some studies find significant reductions, while others find negligible effects. In addition, some studies find that cameras actually increase the amount of violence used by civilians against police officers, and that cameras may increase the most severe forms of force. There are two important caveats to the current research on body worn cameras: First, such devices are in their relative infancy. As a consequence, there are relatively few studies on their effectiveness and most of them only cover a relatively small time period. Second, most of the studies have been carried out in America where levels of violence are considerably higher than in the UK. It will clearly require further research before we can draw firm conclusions on the impact of their use.

James Dobson is a researcher at Bright Blue