His interpretation is how it should be read in English. It may be not how it should have been written. > 78% of black kids had parents who grew up in the top t

His interpretation is how it should be read in English. It may be not how it should have been written. > 78% of black kids had parents who grew up in the top three levels and moved down at least one. Let B = all black kids; BT = black kids who had parents who grew up in the top three levels; BD = black kids who(se parents) moved down at least one level The only way that sentence can be interpreted in English is: |BT ∩ BD| / |B| = 78% If what they wanted to say was: |BT ∩ BD| / |BT| = 78% Then the way to say that in English would have been: > Of the black kids whose parents grew up in the top three levels, 78% moved down at least one.