The World Bank prepares and publishes estimates of the number of poor people in the world. These numbers, particularly the count of people living below $1 a day, are widely quoted and used by the Bank, the press, and by political leaders around the world. They are the raw material in the debate...

Purchasing power parity exchange rates, or PPPs, are price indexes that summarize prices in each country relative to a numeraire country, typically the United States. These numbers are used to compare living standards across countries, by academics in studies of economic growth, particularly...