A large-scale analysis of racial disparities in police stops across the United States

“To assess racial disparities in police interactions with the public, we compiled and analyzed a dataset detailing nearly 100 million municipal and state patrol traffic stops conducted in dozens of jurisdictions across the country—the largest such effort to date. We analyze these records in three steps. First, we measure potential bias in stop decisions by examining whether black drivers are less likely to be stopped after sunset, when a “veil of darkness” masks one’s race. After adjusting for time of day—and leveraging variation in sunset times across the year—we find evidence of bias against black drivers both in highway patrol and in municipal police stops. Second, we investigate potential bias in decisions to search stopped drivers. Examining both the rate at which drivers are searched and the likelihood that searches turn up contraband, we find evidence that the bar for searching black and Hispanic drivers is lower than for searching whites. Finally, we examine the effects of legalizing recreational marijuana on policing in Colorado and Washington state. We find evidence that legalization reduced the total number of searches conducted for both white and minority drivers, but we also find that the bar for searching minority drivers is still lower than for whites post-legalization. We conclude by offering recommendations for improving data collection, analysis, and reporting by law enforcement agencies.”

You can read the full text of the study here.

Key Findings
  • Black drivers are stopped more often than whites, and the degree of disparity is larger among municipal police stops than state police stops. However, Hispanic drivers are stopped at slightly lower rates than white drivers.
  • Black and Hispanic drivers are more likely than white drivers to have their vehicle searched; the authors indicate that “the bar for searching black and Hispanic drivers is generally lower than for searching white drivers.”
  • Jurisdictions should collect individual-level stop data including the date and time of the stop; the location; the race, gender, and age of the driver; the reason for the stop; whether a search was conducted; whether contraband was found; the stop outcome (citation or arrest); and the specific violation the driver was charged with.
  • Police departments should regularly audit their stop data by comparing an officer’s perception of race to a third party’s judgment based on driver’s license photos.
  • Law enforcement agencies should take steps to make data more accessible to the public.
Emma Pierson, Camelia Simoiu, Jan Overgoor , Sam Corbett-Davies, Daniel Jenson, Amy Shoemaker , Vignesh Ramachandran, Phoebe Barghouty, Cheryl Phillips, Ravi Shroff and Sharad Goel, Stanford Computational Policy Lab