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Persistent racial bias influences police stop and search decisions

A study by the Stanford School of Engineering, California, published in May 2020, has found that police stop fewer black drivers at night when a 'veil of darkness' obscures their race.

In what is the largest-ever study of alleged racial profiling during traffic stops, the results have found that black people, who are pulled over more frequently than white people by day, are much less likely to be stopped after sunset when darker settings mask their race.


The same finding applied to members of the Hispanic community.


After the analysis of 95 million traffic stop records, filed by officers with 21 state patrol agencies and 35 municipal police forces from 2011 to 2018, researchers concluded that police stops and search decisions do indeed suffer from persistent racial bias.


The study also found that when drivers were pulled over, the cars of black and Hispanic individuals were searched disproportionately more than for white people.


The findings provide one example of systematic bias that continues to breed racial inequality in the U.S.

Image credit: Verdict

The dataset provided a statistically valid sample based on two important variables: the race of the driver being stopped; and the darkness of the sky at around 7 PM - the specific time of day chosen to analyse traffic stop records.


The analysis left no doubt that the darker it got (as the clocks fell back and the sky grew darker at around 7 PM), the less likely it became that a black driver would be stopped. The reverse was true when the sky was lighter.


Providing some opinion on their findings, the researchers wrote in the May 4 issue of Nature Human Behaviour: "[Our results] point to the value of policy interventions to mitigate these disparities".


In a time where public interest has taken a huge focus on the Black Lives Matter movement, this research stands to support the urgency of the cause and the issues of institutional racism that has helped to create them.


In a significant power move, the research team made their eye-opening data available to the Stanford Open Policing Project to aid investigative and data-savvy reporters and to hold workshops to help reporters learn how to use the data to produce local stories.


So far, around 200 journalists have been trained. The project, which is a collaborative effort, has demonstrated the power of combining data science with journalism to tell important stories and help contribute to societal change.

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