30%, not 40%, according to your article. In the same year (2007), I had just finished my Ph.D. and finished grad school. My income went from about $18k to $50k.
In that year, I had more wealth than the bottom 25% of the American population combined. You probably did too.
25% of the US population has 0 or negative net worth. Combine those and the sum is well south of 0, so if you have a positive net worth, you're worth more than the bottom 25% combined (and then some, because the people with negative net worth would average out some of those positive net worth).
The confusion over this stems from people living comfortable lives, despite negative net worth, because their cash flow satisfies creditors and their expected lifetime net worth (after the debts are finally paid off) is positive.
The statistics are misleading because they view the data as "game over right now", when the matter is ongoing. Someone might have negative worth right now, but that's not taking into account the fact they'll earn a million dollars over the next decade.
In that year, I had more wealth than the bottom 25% of the American population combined. You probably did too.
http://blogs.reuters.com/felix-salmon/2011/12/13/how-alice-w...