After early years of turbulence and despite lacking natural resources and a hinterland, the nation rapidly developed to become one of the Four Asian Tigers based on external trade, becoming a highly developed country; it is ranked ninth on the UN Human Development Index and has the second-highest GDP per capita (PPP) in the world. Singapore is the only country in Asia with a AAA sovereign rating from all major rating agencies. It is a major financial and shipping hub, consistently ranked the most expensive city to live in since 2013, and has been identified as a tax haven. Singapore is placed highly in key social indicators: education, healthcare, quality of life, personal safety, and housing, with a home-ownership rate of 91%. Singaporeans enjoy one of the world's longest life expectancies, fastest Internet connection speeds and one of the lowest infant mortality rates in the world.