Posted on April 22, 2021

The Effects of Black Lives Matter Protests

Jerusalem Demsas, Vox, April 9, 2021

There’s long been a fierce debate about the effect of Black Lives Matter protests on the lethal use of force by police. A new study, one of the first to make a rigorous academic attempt to answer that question, found that the protests have had a notable impact on police killings. For every 4,000 people who participated in a Black Lives Matter protest between 2014 and 2019, police killed one less person.

Travis Campbell, a PhD student in economics at the University of Massachusetts Amherst, released his preliminary findings on the Social Science Research network as a preprint, meaning the study has yet to receive a formal peer review.


From 2014 to 2019, Campbell tracked more than 1,600 BLM protests across the country, largely in bigger cities, with nearly 350,000 protesters. His main finding is a 15 to 20 percent reduction in lethal use of force by police officers — roughly 300 fewer police homicides — in census places that saw BLM protests.

Campbell’s research also indicates that these protests correlate with a 10 percent increase in murders in the areas that saw BLM protests. That means from 2014 to 2019, there were somewhere between 1,000 and 6,000 more homicides than would have been expected if places with protests were on the same trend as places that did not have protests. Campbell’s research does not include the effects of last summer’s historic wave of protests because researchers do not yet have all the relevant data.


To try to further prove his findings are sound, Campbell also shows that before 2014 there were almost parallel trends of police homicides in both the places that would go on to see protests and places that wouldn’t. That suggests that what changed in 2014 and beyond regarding both the reduction in police homicides and the increase in murder — is likely the effect of the BLM protests, not some other hidden variable.

Campbell notes that “BLM did not transform into the protests movement it is known as today until the police killings of Eric Garner in New York City and Michael Brown in Ferguson, MO in 2014,” which is why he begins his research with that year.


The major finding in the paper is that places with BLM protests experienced a statistically significant decline in police homicides. Further, the biggest declines are when protests are relatively large and/or frequent.

Campbell also observes that, over time, the gap in police homicide rates widens between places with and without protests. In year zero, he finds a 13 percent drop in police homicides; by year four, that decline expands by 14 percentage points. That means it’s likely that the effect of BLM protests is strong enough to lower the number of police homicides for several years.

Campbell believes there are three potential mechanisms that could have led to this decline, none of which are mutually exclusive.

First, he observed an increase in the use of body cameras and different types of community policing. It’s possible that, in response to BLM protests, police departments implemented reforms that reduced lethal use of force. Campbell’s research finds a significant increase in the likelihood of an agency obtaining body-worn cameras (55.3 percent), patrol officers within a designated geographic area (20.6 percent), and SARA officers, a type of community policing (57.5 percent).


The second mechanism is that civilians are becoming more wary of the police in the aftermath of these protests and the publicizing of instances of police homicides. That could mean people call 911 less or engage with police officers less of their own volition, which has the effect of reducing civilian/police interactions and thereby fatal interactions as well.

Finally, the third mechanism is something called the Ferguson effect: the supposition that protests against police brutality reduce officer morale and effort due to the “intensified scrutiny from the community and media.” In other words, officers stop doing their jobs as aggressively. This can lead to reduced arrests, especially for less serious crimes like disorderly conduct or marijuana possession.

Deepak Premkumar, a research fellow at the Public Policy Institute of California, found in recently released research that police do reduce their efforts following officer-involved fatalities: Theft arrests fall by 7 percent, and for “quality of life crimes” like disorderly conduct or marijuana possession, arrests decline by up to 23 percent (weed possession alone declines by up to 33 percent).


{snip} Campbell’s study finds that BLM protests correlate with a 10 percent increase in murder. That is, there were a few thousand more homicides in the places where there were BLM protests than would have been expected if those places followed the same trends as the ones that didn’t see protests.


A number of factors could be driving the increase. {snip}


First, it’s possible criminal activity rises in areas that have seen protests because people stop calling the police or working with them out of fear or anger — thereby emboldening criminal behavior. Moreover, some experts believe people will try to resolve their disputes extrajudicially if the system loses legitimacy following a police homicide.

If this were happening, we would expect to see a reduction in the reported rates of low-level crime — fewer low-level crimes would be reported relative to high-level crimes like murders. Murders are less likely to go unnoticed because, well, there’s a missing person and/or a body. So the murder rate is usually the best indicator of what’s actually going on with crime writ large.

Campbell observes a significant increase in the murder rate but a simultaneous 8.4 percent decrease in total property crimes reported. That is consistent with people voluntarily reducing interactions with the police, and other criminologists are in favor of this explanation. {snip}

One other possible explanation for the increased murder rate is that law enforcement officials are the ones voluntarily reducing their interactions with the community and as a result emboldening criminal activity. One way to observe whether police are reducing their efforts is to see whether the share of property crimes cleared falls over this period. In other words, are police not trying as hard — either because they are demoralized or angry at public scrutiny of their behavior — to solve low-level crimes that are reported to them? Campbell observes a 5.5 percent decline in the share of property crimes cleared, which is consistent with police reducing their efforts immediately following the protests.