Police bias may well be a significant problem, but in accounting for why some of these encounters turn into killings, it is swamped by other, bigger problems….

Police killings are a race problem: African-Americans are being killed disproportionately and by a wide margin. And police bias may be responsible. But this data does not prove that biased police officers are more likely to shoot blacks in any given encounter.

Instead, there is another possibility: It is simply that — for reasons that may well include police bias — African-Americans have a very large number of encounters with police officers. Every police encounter contains a risk: The officer might be poorly trained, might act with malice or simply make a mistake, and civilians might do something that is perceived as a threat. The omnipresence of guns exaggerates all these risks.

Such risks exist for people of any race…. But having more encounters with police officers, even with officers entirely free of racial bias, can create a greater risk of a fatal shooting.

Arrest data lets us measure this possibility. For the entire country, 28.9 percent of arrestees were African-American. This number is not very different from the 31.8 percent of police-shooting victims who were African-Americans. If police discrimination were a big factor in the actual killings, we would have expected a larger gap between the arrest rate and the police-killing rate.