I never really got this kind of statistic. Surely the "poorest" people in the world have negative wealth, i.e. they are in debt. But then, such a person isn't necessarily "poor". An American just out of college is probably in debt with little-to-no savings, but she's almost certainly experiencing a better standard of living than some barely-positive wealth Indian subsistence farmer (who would actually prefer to be in debt with an education, but doesn't have access to a financial market).
http://www.forbes.com/billionaires/list/#version:static
75+67+60.8+50+45.2+44.6+43.6+40
That is 426.2 Billion dollars
Earth population is 7 Billion.
Half is 3.5
That gives 121.77 dollars per people
Take that as you will
edit : for reference, China has 1,3 billion people, India has 1,2 billion people and Africa (yes, the continent) has a population of 1,2 billion people