alt Hacker NewsHouseholds with earners in their 20's and early 30's don't tend to have a lot of children of university age. One would want to use the median income of households with university-aged children.
(Median income by age rises sharply from 20->40, then flatlines... the median age of a mother is around 27?)
I'd also think you'd want to adjust by geography based on COL. A two earner family earning $200K in SF or NYC is different than one earning that in suburban Arkansas.