The term "developed country" is often used to describe a sovereign state that possesses a mature economy and a technologically advanced infrastructure—however, this description fails to convey the full breadth and depth of the term. The United Nations Development Programme measures human development in the world's countries by tracking dozens of data points across a vast range of sectors, ranging from GDP per capita to literacy rate, life expectancy, political stability, and access to electricity. These points are then collated into a single score, the annual Human Development Index (HDI).
The HDI ranges from 0.000 (lowest development) to 1.000 (highest development). Countries which score between 1.000 and 0.800 are classified as developed. Countries whose HDI score falls below that are classified as developing, least-developed, or (informally) underdeveloped. HDI can be used to determine the best countries to live in, as more developed countries typically offer their residents a higher quality of life.
Top 10 Developed Countries (2021 HDI):*
*Full list following text.
Why some sources differ on what constitutes a "developed country"
The term "developed country" is often used to describe countries with developed economies or developed markets, which can lead to scenarios in which a given country is considered developed in one sense by one institution, but not in another sense by another institution. For example, the United Nations classifies Turkey as a developed country thanks to its 2021 HDI of 0.838 (Turkey is also a member of the G20, a group composed of countries with the largest economies in the world).
However, organizations including Dow Jones and the Financial Times Stock Exchange Group (FTSE) classify Turkey as an emerging market rather than a developed market. Similarly, the CIA World Factbook follows the World Bank classification system, in which Turkey is classified as an upper-middle income country, which corresponds to a developing economy, rather than a high-income country, which would classify as developed.