A cautionary tale about measuring racial bias in policing

3 min read
Racial bias and policing made headlines last year after a study examining records of fatal police shootings claimed white officers were no more likely to shoot racial minorities than nonwhite officers. There was one problem: The study was based on a logical fallacy.
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The original research counted the numbers of fatal shootings, but never considered how often civilians encounter police officers, an essential ingredient to justifying its central claim.

The findings sparked a fiery debate among other academics, including two professors from Princeton University, who raised mathematical concerns about the study's approach. Today, they published their critique as a letter in the Proceedings of the National Academy of Sciences (PNAS).

The pair—Dean Knox, assistant professor of politics, and Jonathan Mummolo, assistant professor of politics and public affairs— outline a number of serious flaws in the original study, which was featured in PNAS on Aug. 6, 2019.

For the original study, researchers from Michigan State University and the University of Maryland compiled data on 900 fatal U.S. police shootings from crowdsourced databases. They then contacted each police department, gathering information about the race of the police officers responsible for each fatality.

The researchers then used the shootings data to predict the race of victims. Specifically, they showed that when the shooting officer was black, the civilian who was shot was more likely to be black than white. And controlling for attributes of the county in which shootings occurred, "the relationship between officer and…
Science X staff
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