ACT Senators). Senators for the states serve six-year terms, with half the senators from each state usually being elected at each federal election. The terms of the territory senators coincide with the duration of the House of Representatives. The Senate is elected both proportionately and preferentially, except that each state has an equal number of seats so that the distribution of seats to states is non-proportional to the total Australian population. Thus, although within each state the seats proportionally represent the vote for that state, overall the less populous states are proportionally stronger in representation for their population compared to the more populous states. At the 2013 federal election, the Senate election, contested by over 50 groups, saw extensive "preference deals" (legitimate manipulation of group voting tickets), resulting in the election to the Senate of Ricky Muir from the Australian Motoring Enthusiast Party, who had received only 0.5% of first-preference support. This exploitation of the system was alleged to undermine the entitlement of voters "to be able to make real choices, not forced ones—and to know who they really are voting for". Following the 2013 election, the Abbott Liberal government announced it would investigate changing the electoral system for the Senate in order to prevent the preference system being abused. On 22 February 2016, the Turnbull Liberal government announced several proposed changes. The changes had the support of the Liberal/National Coalition, the Australian Greens, and Nick Xenophon − a three-vote majority. The Senate reform legislation passed both houses of the Parliament of Australia on 18 March 2016 after the Senate sat all night debating the bill. The changes abolished group voting tickets and introduced optional preferential voting, along with party logos on the ballot paper. The ballot paper continues to have a box for each party above a heavy line, with each party's candidates in a column below that party's box below the solid line. Previously, a voter could either mark a single box above the line, which triggered the party's group voting ticket (a pre-assigned sequence of preferences), or place a number in every box below the line to assign their own preferences. As a result of the changes, voters may assign their preferences for parties above the line (numbering as many boxes as they wish), or individual candidates below the line, and are not required to fill all of the boxes. Both above and below the line voting