The international poverty line has just been raised to $1.90 a day, but global poverty is basically unchanged. How is that even possible?

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.