70%

"It's the youngest and poorest who have the most to worry about. Families headed by people under 35 are almost 70 percent poorer today, adjusting for inflation, than they were in 1984. The causes: lower wages, more expensive housing, and student debt."
--David Frum, "America the Anxious: Why We’re Freaking Out"
Newsweek, August 13/20, 2012, page 41

Also available online,

http://www.thedailybeast.com/newsweek/2012/08/05/david-frum-on-high-anxiety-america.html

(Alas, the source of this eye-opening statistic is not revealed...)