Downward Mobility For African Americans?

Some brutal data:

Overall, family incomes have risen for both blacks and whites over the past three decades. But in a society where the privileges of class and income most often perpetuate themselves from generation to generation, black Americans have had more difficulty than whites in transmitting those benefits to their children.

Forty-five percent of black children whose parents were solidly middle class in 1968 -- a stratum with a median income of $55,600 in inflation-adjusted dollars -- grew up to be among the lowest fifth of the nation's earners, with a median family income of $23,100. Only 16 percent of whites experienced similar downward mobility. At the same time, 48 percent of black children whose parents were in an economic bracket with a median family income of $41,700 sank into the lowest income group.

But Booker Rising blogger Shay has some methodology questions.