Here is an interesting study that shows how world poverty rates are calculated, but also demonstrates that those who live on less than $1 /day have decreased around the world:
"World poverty is falling. Between 1970 and 2006, the global poverty rate has been cut by nearly three quarters. The percentage of the world population living on less than $1 a day (in PPP-adjusted 2000 dollars) went from 26.8% in 1970 to 5.4% in 2006"