Now, instead of focusing on police use of force, some researchers are turning their attention to use of language.
More research is needed to determine whether this racial disparity in language occurs in other communities across the United States, but Rob Voigt, lead author of the study, said it's worth investigating.
"At the very least, this provides evidence for something that communities of color have reported, that this is a real phenomenon," said Voigt, a doctoral student in the linguistics department at Stanford University.
Voigt added that he and his colleagues were grateful to the Oakland Police Department for allowing them to study the department's body camera footage.
"We're also hoping it inspires police departments to consider cooperating with researchers more. And facilitating this kind of analysis of body camera footage will help police departments improve their relationship with the community, and it will give them techniques for better communication," he said. "When people feel they're respected by the police, they are more likely to trust the police
, they are more likely to cooperate with the police, and so on and so forth. So we have reason to expect that these differences that we find have real-world effects."
A racial disparity, hidden in language
The study involved 183 hours of body camera footage taken during 981 routine traffic stops by 245 different Oakland Police Department officers in April 2014. The footage of the officers' interactions with community members was transcribed.
The researchers then randomly selected 312 utterances spoken to black community members and 102 spoken to white community members for volunteers to analyze.
The researchers asked the volunteers to read the transcript of one community member's utterance and then the utterance by the police officer that followed in response. The volunteers rated on a four-point scale how respectful, polite, friendly, formal and impartial the officer was.
Each interaction was rated by at least 10 volunteers, who did not know the names or races of the officers or the community members or any other contextual or identifying information.
Next, the researchers developed a computer model to rate how respectful each interaction was based on pre-existing scientific literature about respectfulness and politeness.
For instance, the computer measured how often police officers introduced themselves; used formal titles such as ma'am or sir; used words like please and thank you; apologized, such as saying "sorry to stop you"; and reassured safety, such as saying "drive safe, please" -- all of which are utterances that show signs of respect, according to the study.
For example, the transcripts in the study included these sentences: "Sorry to stop you. My name's Officer (name) with the Police Department." "There you go, ma'am. Drive safe, please."
Less respectful utterances included using informal titles like "man" or first names, or asking for agency, such as saying "do me a favor."
The transcripts in the study included these sentences: "All right, my man. Do me a favor. Just keep your hands on the steering wheel real quick." "(First name] can I see that driver's license again?"
The researchers used the computer model to automatically estimate the level of respect for every utterance and to estimate how respectful a human might have rated each utterance.
After analyzing all of their data, the researchers found that white community members were 57% more likely to hear an officer say one of the most respectful utterances in the dataset, such as apologizing. Black community members were 61% more likely to hear an officer say one of the least respectful utterances, such as informal titles.
The racial disparity occurred despite the police officers' race and among most officers, not outliers, the researchers found. The disparity emerged at the early onset of interactions and was still present after controlling for whether a community member was arrested, given a citation or searched, Voigt said.
'This is our effort to build trust,' deputy chief says
"From our perspective, we appreciate the fact that we are able to participate in this study where we were actually able to assess our officers' interactions and their communications and see ways in which we can improve," Oakland Police Department Deputy Chief Leronne Armstrong said Tuesday.
"The data that they were using was from 2014," he said of the study. "Since that time, we've implemented lots of training internally, both for our sworn officers as well as our professional staff."
Armstrong said posters displaying the four principles of procedural justice
-- giving a voice to the community, being neutral in decision-making, respectfulness and trustworthiness -- have been posted throughout the police department's building.
"We want our officers to understand that these things, according to the research, matter to people and that they help officers build trust with community members," Armstrong said.
"We hope that departments throughout the country will understand the importance of taking an internal look at themselves," he said. "It's not a bad thing to learn. It is not a bad thing to improve, and it is vital when you're trying to build trust. This is our effort to build trust and just be the best we can be for the city of Oakland."
The study "is self-limiting in the sense that they focused only on transcriptions of verbal utterances in traffic stops, but I think this is a wise first step," said Jack Glaser, a professor of public policy at the University of California, Berkeley, who was not involved in the study.
"I am aware of community surveys that have been conducted, and they certainly indicate that black people feel treated more poorly by police, but this is the first analysis of body-worn camera data that I'm aware of," he said. "It contributes a lot to our understanding of racial disparities in police-civilian encounters."
Glaser added that interactions in which a community member might feel disrespected not only can be stressful but can lead to behavioral and health effects and even acute trauma for that community member.
John Dovidio, a professor at the Yale School of Public Health, agreed.
'How can you change the training?'
"If any of us feel that we've been disrespected in the situation, it's psychologically wounding to us," said Dovidio, who was also not involved in the new study.
He added, however, that respect appears to be a particularly deep-rooted need for communities that historically have been disadvantaged.
"If you bring a majority and a minority group member together, a white and a black person, in those interactions, the basic needs and goals of the white and black person are very different," Dovidio said.
"The white person in these intergroup interactions tends to want to be liked. They want to be sort of affirmed as being a good person," he said. "But people of color, and this occurs for other historically disadvantaged groups, their major goal is to be respected. ... Everybody wants respect, but minority group members in interracial interactions with authority figures have a particularly heightened need to feel respected in those interactions, and that's why respect is such a key variable."
The first step to improving everyday interactions between police and the communities they serve is awareness, which the new study provides, Dovidio said.
"What this does is, makes it real, makes it tangible, makes it objective," he said. "It can then be used not to blame people ... but what it can be used for is a tool for teaching people how to not do something that they may be doing unintentionally."
In other words, police and other people of authority tend to unconsciously or implicitly display this disrespect through language, Dovidio said.
"The outcome of this disrespect is actually, it's a lose-lose situation, because law-abiding people in a community don't want crime. Police don't want crime. But the actions of the police officers undermine the trust and connection of them with the community," Dovidio said.
"Rather than blame police officers, I think the question is, how can you change the training and the experiences that police officers have?" he said. "I would hope that this article is not interpreted as a way of saying police officers are bad, but rather, here's some ideas of how police training can be improved and police practice can be improved to get the trust of the community, to create a relationship that's healthy and cooperative."