The World Bank Group assigns the world’s economies to four income groups: low, lower-middle, upper-middle, and high. The classifications are updated each year on July 1, based on the GNI per capita of the previous calendar year. GNI measures are expressed in United States dollars using conversion factors derived according to the Atlas method, which in its current form was introduced in 1989. The World Bank’s income classification aims to reflect a country’s level of development, drawing on Atlas GNI per capita as a broadly available indicator of economic capacity.