Nigeria is the most populous country in Africa and the seventh most populous country in the world, with an estimated 206 million inhabitants as of late 2019. It has the third-largest youth population in the world, after India and China, with nearly half its population under the age of eighteen. Nigeria's economy is the largest in Africa and the 24th largest in the world, worth almost $450 billion and $1 trillion in terms of nominal GDP and purchasing power parity, respectively. [Note 2] Nigeria is often referred to as the "Giant of Africa", owing to its large population and economy, and is also considered to be an emerging market by the World Bank; it has been identified as a regional power on the African continent, a middle power in international affairs, and has also been identified as an emerging global power. However, its Human Development Index ranks 158th in the world, and the country is classified as a lower middle-income economy, with a gross national income per capita between $1,026 and $3,986.