Think about the impact of an arrest though. If one group is getting arrested at a higher rate and thus likely to be convicted of some type of offense, they could be more likely to later reoffend given they now have a conviction on their record and are less likely to be able to find a reasonable job. It is a vicious spiral. A while back, there was a police shooting at a traffic stop (the guy sped off) and it turned out he had been arrested 21 times. I have zero evidence, but my feeling is that the same types of infractions folks in one community are pulled over for are glossed over in others (missing front license plate, tail light out), which starts the vicious cycle.