Bias in Traffic Stops and Searches

Going back as far as 1999 when the data was available and as recently as 2018, Stanford’s Open Policing Project quantified what most people of color already knew. An excerpt from one of the publications coming out of that study:

We assessed racial disparities in policing in the United States by compiling and analysing a dataset detailing nearly 100 million traffic stops conducted across the country. We found that black drivers were less likely to be stopped after sunset, when a ‘veil of darkness’ masks one’s race, suggesting bias in stop decisions. Furthermore, by examining the rate at which stopped drivers were searched and the likelihood that searches turned up contraband, we found evidence that the bar for searching black and Hispanic drivers was lower than that for searching white drivers. Finally, we found that legalization of recreational marijuana reduced the number of searches of white, black and Hispanic drivers—but the bar for searching black and Hispanic drivers was still lower than that for white drivers post-legalization. Our results indicate that police stops and search decisions suffer from persistent racial bias and point to the value of policy interventions to mitigate these disparities.

Pierson,Emma, Simoiu,Camelia, Overgoor,Jan, Corbett-Davies,Sam, Jenson,Daniel,
Shoemaker,Amy, Ramachandran,Vignesh, Barghouty,Phoebe, Phillips,Cheryl, Shroff,Ravi and Goel,Sharad. (2020) A large-scale analysis of racial disparities in police stops across the United State. Nature Human Behavior. https://doi.org/10.1038/s41562-020-0858-1 *

The study itself has some awesome data sets you can manipulate online or download.

It’s also telling that the legalization of marijuana has an impact on the data. Below is the graph showing the disparity of searches and stop before and after legalization.

In Washington and Colorado, far fewer people — both white and minority drivers — are searched overall. However, the racial disparities in searches remain and there is a persistent gap in the threshold for searching white and minority drivers. Source: https://openpolicing.stanford.edu/findings/


* Although I normally try to add these references in as close to APA format as I can, if all the authors of a paper are available, I’m going to post them and not stop at the first 6, as APA dictates. Also, I post the full names of the authors because, well, I think they deserve it.

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