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A new study of police interactions has found, yet again, that black drivers are stopped by police more often than white drivers.

The study, led by Stanford psychologist Jennifer Eberhardt, isn't the first study to draw a similar conclusion. In 2014, the Washington Post analyzed federal data that showed that 13% of black drivers said they had been had been pulled over, compared with 10% of white drivers. Last fall, the New York Times found that black drivers in Greensboro, N.C. were being pulled over "at a rate far out of proportion with their share of the local driving population."

But the new Stanford study is the most complete examination yet of the interactions police officers have with drivers of different races. Thanks to a federal court order demanding that the Oakland Police Department reform its policing practices, Eberhardt had unprecedented access to every aspect of police-motorist interactions in Oakland stretching for an entire year, including audio recordings of 28,119 police encounters.

One of the Stanford study's most interesting findings was about language—specifically, that African-Americans were spoken to more casually than whites were during traffic stops, perhaps suggesting an ingrained lesser degree of respect toward them.


With black motorists, officers were more likely to use words like "hey" as opposed to "hello," "man" as opposed to "sir," and colloquialisms such as "gonna," "got to," and ''ain't," the report said. While the officers did appear more likely to say "thank you" to black people, previous analyses suggest that officers also ask more questions of black people, giving them more occasions to thank drivers for answering.

Here were common word choices found in audio recordings of traffic stops over a one-month period:


White drivers were more likely to hear procedural language like “citation” or “registration” from police officers, and were more likely to hear words focused on the actual offense, such as “illegal left,” running a “red light,” and being on the “phone.” Officers are also more likely to tell white drivers that they can “contest” a citation, and more likely to comment on “the reason” for the stop.

The Stanford team also compared usage of the words "probation" and "parole" at stops. When issuing a citation, cops were ten times more likely to use either word for black people.


Using all this data, the researchers were actually able to predict the race of a police subject without prior knowledge of their race 68% of the time.


These kind of disparities helped result in 60% of police stops in Oakland (nearly 17,000) affecting African Americans, more than three-times that of the next most common group, Hispanics, and almost six-times that of whites.

Despite her findings, Eberhardt does not believe the Oakland Police Department is filled with racists. Rather, she believes the phenomena are the result of institutional, decades-old biases and ingrained behaviors and police practices.


"We found little evidence that disparate treatment arose from explicit racism or purposeful discrimination," she writes. "Instead, our research suggests that many subtle and unexamined cultural norms, beliefs, and practices sustain disparate treatment."

The causes for these racial disparities in language are numerous, Eberhardt said. While implicit bias is certainly a factor,  the cultural norms and practices within law enforcement agencies, officers’ perceptions of what their superiors want them to do, and institutional incentives that direct officers to focus more of their time on certain types of enforcement (e.g. arrests) and less on positive community contact all influence these outcomes.


But they can be overcome. Eberhardt and her team laid out 50 recommendations for the OPD to reduce racial disparities in policing, including undergoing training to make officers more aware of their internalized biases, and having more day-to-day positive interactions with at-risk communities.

The changes are unlikely to happen overnight, but it's clear we need more studies like these to get at the underlying causes of a nationwide phenomenon.


Rob covers business, economics and the environment for Fusion. He previously worked at Business Insider. He grew up in Chicago.