• On basis of income , the World Bank divides the world's economies into four income groups:  high, upper-middle, lower-middle, and low.
• The income classification is based on a measure of national income per person, or GNI per capita, calculated using the Atlas method.
• In 1978, the first World Development Report introduced groupings of "low income" and "middle income" countries using a threshold of $250 per capita income as threshold between the groups.
• In the 1983 WDR, the "middle income group" was split into "lower middle" and "upper middle" groups, and in 1989 a "high income" country definition was introduced.
• Since then, the thresholds to distinguish between the income groups have been adjusted for prices over time.
• As of 1 July 2019,

o  Low-income economies - GNI per capita is $1,025 or less

o  Lower middle-income- GNI per capita between $1,026 and $3,995

o  Upper middle-income economies- $3,996 and $12,375

o  High-income economies - GNI per capita of $12,376 or more.

• WDR or World Development Report is published by World Bank annually.