World Bank researchers have been trying to assess the extent of extreme poverty across the world since 1979 and more systematically since the World Development Report 1990, which introduced the dollar-a-day international poverty line. From the beginning, the idea was to measure income poverty with respect to a demanding line which, first, reflects the standards of absolute poverty in the world’s poorest countries and, second, corresponded to the same real level of well-being in all countries. The first requirement led researchers to anchor the international poverty line on the national poverty lines of very poor developing countries. And the second requirement led them to use purchasing power parity exchange rates (PPPs) – rather than nominal ones - to convert the line into the US dollar and, more importantly, into the currencies of each developing country.
A fascinating feature of purchasing power parity (PPP) is more people hold an opinion on it than know what it means. This was in ample display last week, when the Global Office of the International Comparison Program (ICP), hosted by the World Bank, announced the latest PPP data for the world, pertaining to 2011.
Putting aside complexities, PPPs may be viewed as an estimate what one US dollar can buy in different countries. In case a dollar in Ghana can buy three times what it can buy in the United States, then a person who earns 1,000 dollars each month in Ghana is said to earn 3,000 in terms of ‘PPP-adjusted dollars’.