(Jose Luis Gonzalez/Reuters)

At City Journal, Heather Mac Donald has a troubling rundown of a congressional hearing on policing she participated in. Another witness, Phillip Atiba Goff of the Center for Policing Equity, claimed that the authors of two different studies — both of which had found no anti-black bias in the use of lethal force by police — had conceded that their work was severely flawed. To the contrary, the authors of those studies have doubled down on their central claims in subsequent papers.


Academic spats aside, I wanted to do a quick walkthrough here of the more recent study Goff attacked — which was published in the Proceedings of the National Academy of Sciences in August and has been controversial ever since. (Full disclosure, I’m borrowing liberally from a Twitter thread I wrote when the study first came out.)

The main question we want to answer about this topic is this: If a black person and a white person behave the same way in the same situation, is the black person more likely to be shot by a cop? The biggest criticism of the study is that it doesn’t directly answer this question.

The dataset the authors use is made up purely of cases where people were shot. It doesn’t include any non-fatal interactions with police, so it can’t be used to look at the differences in behavior between the folks who got shot and the folks who didn’t. Rather, the study’s main contribution (similar to an earlier one I wrote about here) is to see what we can learn from the race of the officers in these shootings.


It’s a reasonably safe assumption that black officers are less likely than white officers to hold anti-black racist beliefs. So if anti-black racism is driving lots of shootings of black suspects, shootings of black suspects should be relatively unlikely to involve black officers.


In the simplest analysis, the opposite is actually the case: Black suspects are disproportionately killed by black officers. But this isn’t as odd as it seems, because some parts of the country have higher black populations than others. In those places, both suspects and officers are more likely to be black.

The study addresses this by statistically controlling for the demographics of homicide victims in each county where a shooting happened — and the correlation between officer and suspect race disappears. In other words, someone shot by the police is more likely to be black if the area has a lot of black homicide, but not if the police officer involved happened to be white. This is inconsistent with the idea that white cops are killing black suspects out of anti-black racism.


One of the biggest limitations to this approach, however, is that black cops might disproportionately patrol black neighborhoods even within counties. If this is the case, black suspects and black officers might encounter each other more — above and beyond what’s accounted for in the statistical controls — which could cancel out the effects of white cops’ racism. To put it differently, black cops could shoot black suspects simply because they encounter a lot of black suspects, while white cops could shoot black suspects out of racism. And if these two phenomena occurred to roughly the same degree, the study would indicate that black and white cops are about equally likely to shoot black suspects.

But this is not some fatal limitation that renders the study useless. It’s a limitation no worse than most studies have, a reason to keep reading future work and not see the issue as settled.