The Pew Research Center recently posted a study analyzing the distribution of income around the world. The study analyzed data from World Bank and Luxembourg Income Study databases and assessed how many people in different countries fell into each of five income brackets in 2001 and 2011.
Pew defined their poor income bracket as people living on less than $2 per day, in line with widely accepted definitions of global poverty. The low income bracket was made up of people living on between $2 and $10 per day, middle-income was between $10 and $20 per day (which includes Americans living at the US government's official poverty line), upper-middle income was between $20 and $50 per day, and high income was over $50 per day.
Because of the global nature of the study, Pew used "purchasing power parity" currency conversion rates, which reflect the differential cost of living between countries. Pew's analysis showed that in 2011, 15% of the world population was living on less than $2 per day, and 56% between $2 and $10. The proportion of the world living in extreme poverty fell almost by half between 2001 and 2011, with millions of people moving from the poorest income bracket into the low-income bracket:
For more, check out Pew's report here.
