Within the IAVS, we follow established classification of countries into low-, middle- and high-income according to their annual GDP (per capita PPP), in the following way:
 

• Low-income countries: GDP <$10,000,
• Middle-income countries: GDP $10,000-24,999,
• High-income countries: GDP $25,000 and more.

Estimates of GDP are based on The World Factbook, compiled by the U.S. Central Intelligence Agency. The table currently used within IAVS can be downloaded here: Comparison of countries by GDP (February 2020).