Are Black Drivers Searched Unfairly In North Carolina?

Over at the Monkey Cage, John Sides interviews Frank Baumgartner, Derek Epp and Kelsey Shoub, authors of Suspect Citizens, a book about traffic stops based on an enormous dataset from North Carolina. Here’s an excerpt:

A key topic in the book is who is targeted for traffic stops. What did your findings reveal about racial disparities in both who gets stopped and what happens during the stop?

….Just by getting in a car, a black driver has about twice the odds of being pulled over, and about four times the odds of being searched.

….You note in the book that these racial disparities would be less noteworthy if they were simply due to underlying differences in criminality. But that’s not the case, correct?

It certainly does not appear to be the case. African Americans are much more likely to be searched after a stop than white drivers, but less likely to be found with drugs, guns, alcohol or other forms of contraband after discretionary searches….Contraband hit rates are 36, 33 and 22 percent for whites, blacks and Hispanics, respectively.

This is very misleading. Take a look at the following illustration. Each square represents a car and each red X represents a car with contraband. The shaded squares show traffic stops:

In this example, blacks and whites both have the same amount of contraband: 12 cars out of 100. However, because the police pull over more black drivers, they find contraband in six cars instead of four. The higher contraband rate is evidence of nothing but unfairness. It’s only higher because police are randomly pulling over more black drivers. But there are actually two plausible explanations for this:

  • Black and white drivers have about the same amount of contraband.
  • Police officers aren’t pulling over cars at random. They have a pretty good sense of who’s carrying contraband and who isn’t, and for both blacks and whites they have a hit rate of about one-third. In other words, they’re treating both blacks and whites with a similar sense of suspicion, and the result is that they’re searching four times as many black drivers and finding four times as much contraband.

We would need more evidence to know which of these is true. But in terms of how “strictly” North Carolina cops apply their contraband sense, it appears to be about the same for blacks and whites, thus the similar percentage of contraband found. In raw numbers this means they’re finding four times as much contraband per car for blacks vs. whites, but this might be because black drivers have a lot more contraband.

In any case, these numbers by themselves don’t prove anything one way or another and we shouldn’t pretend otherwise. However, there is one exception: Hispanics have a much lower contraband hit rate than either blacks or whites. This really does suggest that police are applying a stricter sense of “suspiciousness” to Hispanics, and it’s not panning out.