Each state has a unicameral State Legislative Assembly whose members are elected from single-member constituencies. State governments are led by Chief Ministers, who are state assembly members from the majority party in the assembly. In each of the states with a hereditary ruler, the Chief Minister is normally required to be a Malay, appointed by the ruler upon the recommendation of the Prime Minister. Parliamentary elections are held at least once every five years, the most recent of which took place in May 2013. Registered voters of age 21 and above may vote for the members of the House of Representatives and, in most of the states, for the state legislative chamber. Voting is not mandatory. Except for state elections in Sarawak, by convention state elections are held concurrently with the federal election.