Area: Encyclopedia Britannica
Population, urban population, percentage of population under 15, annual population increase, life expectancy: Toshiko Kaneda, Charlotte Greenbaum, and Kelley Kline, 2020 World Population Data Sheet (Washington, D.C.: Population Reference Bureau, 2020)
Capital, date of origin, literacy rate, per capita GDP: The World Factbook (C.I.A.)
Languages: The World Factbook (C.I.A.); World Book Encyclopedia
Political system: Based on information from Freedom House (a nonprofit human rights organization) and its annual publication, Freedom in the World (2020); Encyclopedia Britannica; and news accounts
Head of government (as of August 2021): Based on information from the GeoCities “Rulers” website (rulers.org); The World Factbook (C.I.A.); and news accounts
HDI: Human Development Report 2020 (United Nations Development Program)
All figures are the latest available from each source for each country; all information is as of May 2021 unless otherwise noted.