The development of a country is measured with statistical indices such as income per capita (per person), gross domestic product per capita, life expectancy, the rate of literacy, freedom index and others. The term low and middle-income country are often used interchangeably but refers only to the economy of the countries. The World Bank classifies the world's economies into four groups, based on gross national income per capita: high, upper-middle, lower-middle, and low income countries. Least developed countries, landlocked developing countries and small island developing states are all sub-groupings of developing countries. Countries on the other end of the spectrum are usually referred to as high-income countries or developed countries.
