"Race" means almost nothing scientifically. Race is a social construct, not a scientific one. All humans are mutts. There may be genetic tendencies revolving around the frequency of certain genes for a given region, but the variations all blur into each other and don't respect borders.
And what does "African American" mean exactly? We are all from Africa if you go back far enough. A history of slavery has been suggested as a way to identify "black," but the ancestry and migration records of many slaves are lost to antiquity. There may be records that can prove one is related to a slave, but that's not the same as being related to somebody of African origins. Not all slaves were from Africa. Thus, there is no clean, fair, and reliable measurement for "black" or any other race.