You left out a variable: black people make up what percentage of that population of that city? If it's, I dunno, the approximately 15% that I would guess it to be, then that's a significantly large number of stops in comparison to white folk.
It's all fun and games until Bayes comes to play. They didn't state the city, but simply said a "Medium Diversity City." Indianapolis is roughly medium at 30% black population although the country average is 13.6%. So the probability of a car containing a black person is roughly 1:3. This means that if you put a random car in front of an officer they are 6 times more likely to stop a black person in this study. Then after that there is such a huge difference in how the stops are handled.
The TableS1 in the data for the study is telling. It's no wonder they don't want to collect statistics on how policing is handled. It's downright damning.
