or government company: the Central Provident Fund Board, the Housing and Development Board, the Jurong Town Corporation, the Monetary Authority of Singapore, Temasek Holdings, or GIC Private Limited (formerly known as the Government of Singapore Investment Corporation); as the most senior executive of a company with an average of $500 million in shareholders' equity for the most recent three years in that office, and which is profitable after taxes; or in any other similar or comparable position of seniority and responsibility in any other organisation or department of equivalent size or complexity in the public or private sector which has given him such experience and ability in administering and managing financial affairs as to enable him to carry out effectively the functions and duties of the office of President. Because of the high requirements needed to run for presidential elections, many presidential elections have been uncontested. All presidential elections have been walkovers except for the first one, held in 1993 which was contested by two people, and the 2011 one, contested by four people. The first presidential election was won by Ong Teng Cheong, a former member of the PAP. Subsequent presidential elections in 1999 and 2005 have been won by S. R. Nathan through walkovers. The 2011 presidential election was contested by Tony Tan Keng Yam, Tan Cheng Bock, Tan Jee Say and Tan Kin Lian. All candidates except Tan Jee Say were former members of the PAP, whose closest relation to the party was when he served as then-Deputy Prime Minister Goh Chok Tong's principal private secretary from 1985 to 1990. The election was won by Tony Tan with a margin of 0.34% over Tan Cheng Bock. 2011 presidential election results 2017 presidential election The 2017 presidential election was won by Halimah Yacob through an uncontested walkover. Referendums A referendum may also be held for important national issues, although it has been held only once in Singapore's political history for the 1962 merger referendum. Calls for a national referendum has been made since then, including the issue over the building of casinos in Singapore. Past elections Legislative Council elections 1948 general election 1948 Rural West by-election 1951 general election 1952 Seletar by-election Legislative Assembly elections 1955 general election 1957 by-elections 1959 general election 1961 by-elections (April and July) As State of Malaysia 1963 general election 1965 Hong Lim by-election Parliamentary elections 1966 by-elections (January, March & November) 1967