internationally for tourism and business purposes. The Orchard Road district, which contains multi-storey shopping centres and hotels, can be considered the centre of shopping and tourism in Singapore. Other popular tourist attractions include the Singapore Zoo, River Wonders and Night Safari. The Singapore Zoo has embraced the open zoo concept whereby animals are kept in enclosures, separated from visitors by hidden dry or wet moats, instead of caging the animals, and the River Wonders has 300 species of animals, including numerous endangered species. Singapore promotes itself as a medical tourism hub, with about 200,000 foreigners seeking medical care there each year. Singapore medical services aim to serve at least one million foreign patients annually and generate US$3 billion in revenue. Demographics As of mid-2018, the estimated population of Singapore was 5,638,700 people, 3,471,900 (61.6%) of whom were citizens, while the remaining 2,166,800 (38.4%) were permanent residents (522,300) or international students, foreign workers, or dependants (1,644,500). According to the country's 2010 census, nearly 23% of Singaporean residents (i.e. citizens and permanent residents) were foreign born; if non-residents were counted, nearly 43% of the total population were foreign born. The same census also reports that about 74.1% of residents were of Chinese descent, 13.4% of Malay descent, 9.2% of Indian descent, and 3.3% of other (including Eurasian) descent. Prior to 2010, each person could register as a member of only one race, by default that of his or her father, therefore mixed-race persons were solely grouped under their father's race in government censuses. From 2010 onward, people may register using a multi-racial classification, in which they may choose one primary race and one secondary race, but no more than two. The median age of Singaporean residents was 40.5 in 2017, and the total fertility rate is estimated to be 0.80 children per woman in 2014, the lowest in the world and well below the 2.1 needed to replace the population. The government has attempted to increase fertility with limited success, as well as adjusting immigration policy to maintain its working-age population. 91% of resident households (i.e. households headed by a Singapore citizen or permanent resident) own the homes they live in, and the average household size is 3.43 persons (which include dependants who are neither citizens nor permanent residents). However, due to scarcity of land, 78.7% of resident households live in subsidised, high-rise, public housing apartments developed by the Housing and Development