Australia is the world's smallest continent, with a total area of 7,686,850 sq km. It is the world's sixth-largest country, with a population of 19,169,083 (July 2000) concentrating along the eastern and southeastern coasts. Its age structure consists of 21% in the 0-14 years group, 67% in the 15-64 years group, and 12% in the 65 years and over, within the ethnic groups of Caucasian (92%), Asian (7%), aboriginal and other (1%). Australia became a commonwealth of the British Empire in 1901. A referendum to change Australia's status, from a commonwealth headed by the British monarch to an independent republic, was defeated in 1999.