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. This in turn suggests that removing police racial bias will have little effect on the killing rate. Suppose each arrest creates an equal risk of shooting for both African-Americans and whites. In that case, with the current arrest rate, 28.9 percent of all those killed by police officers would still be African-American. This is only slightly smaller than the 31.8 percent of killings we actually see, and it is much greater than the 13.2 percent level of African-Americans in the overall population - www.nytimes.com