Of course, that's just an illustration; people don't mechanically drop down a quartile by getting more education.
A 3rd quartile candidate with "some college"earning $1085 a week becomes a second-quartile BA holder earning . . . $1066.
c.1500, originally in astronomy; see quartile (adj.). In statistics, from 1879.
mid-15c., "90 degrees apart" (of astronomical measurements), from Middle French quartil, from Medieval Latin quartilus "of a quartile," from Latin quartus "fourth" (see quart).