Nigeria's economy is the largest in Africa, the 27th-largest in the world by nominal GDP, and 25th-largest by PPP. Nigeria is often referred to as the Giant of Africa owing to its large population and economy and is considered to be an emerging market by the World Bank. It is a regional power in Africa, a middle power in international affairs, and is an emerging global power. However, the country ranks very low in the Human Development Index and remains one of the most corrupt nations in the world. Nigeria is a founding member of the African Union and a member of many international organizations, including the United Nations, the Commonwealth of Nations, NAM, the Economic Community of West African States, and OPEC. It is also a member of the informal MINT group of countries and is one of the Next Eleven economies.