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


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.

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Fig. 1: Geographic coverage of compiled traffic stop data.
Fig. 2: An illustration of the veil-of-darkness test for stops occurring in three short time windows in a single state, Texas.
Fig. 3: Hit rates and inferred search thresholds by race and location.
Fig. 4: Percentage of stops that resulted in a search before and after recreational marijuana was legalized in Colorado and Washington at the end of 2012.
Fig. 5: Percentage of stops that resulted in a search in 12 states in which recreational marijuana was not legalized.

Data availability

All data to reproduce the findings of this study are available at https://openpolicing.stanford.edu.

Code availability

All code to reproduce the findings of this study is available at https://openpolicing.stanford.edu.


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We thank B. Bonilla, W. Kim, J. Nudell, S. Robertson and E. Sagara for their assistance throughout this project; we also thank A. Chohlas-Wood and A. Feller for their helpful feedback. This work was supported in part by the John S. and James L. Knight Foundation and by the Hellman Foundation. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

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E.P., C.S., J.O., S.C.-D., D.J., A.S., V.R., P.B., C.P., R.S. and S.G. designed research, performed research, analyzed data, and wrote the paper.

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Correspondence to Sharad Goel.

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Pierson, E., Simoiu, C., Overgoor, J. et al. A large-scale analysis of racial disparities in police stops across the United States. Nat Hum Behav (2020). https://doi.org/10.1038/s41562-020-0858-1

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