The distinguishing feature of plurality-majority systems is that they almost always use single-member districts. In a First Past the Post system, the winner is the candidate with a plurality of votes, but not necessarily an absolute majority of the votes. When this system is used in multi-member districts it becomes the Block Vote. The Alternative Vote and Majority-Runoff systems are single-member systems that ensure that the winning candidate receives an absolute majority of votes cast.

• Alternative Vote (AV)

  • A preferential, plurality-majority system used in single-member districts in which voters rank their preferences among the candidates. If there is no absolute majority of first choices, the lowest polling candidate is disqualified, his ballots are re-allocated according to the subsequent individual choices of his voters, and the ballots are recounted. The elimination, re-allocation, and recounting steps are repeated until one candidate achieves an absolute majority of votes cast. Whenever a preference is expressed for a candidate who has already been eliminated, the voter's subsequent preference is used.

• Block Vote (BV)

  • A plurality-majority system used in multi-member districts in which electors have as many votes as there are candidates to be elected. Voting can be either candidate-centred or party-centred. Counting is identical to a First Past the Post system, with the candidates with the highest vote totals winning the seats.

• First Past the Post (FPTP)

  • The simplest form of plurality-majority electoral system, using single-member districts, a categorical ballot and candidate-centred voting. The winning candidate is the one who gains more votes than any other candidate, but not necessarily a majority of votes.

• Majority-Plurality (Two-Round System)

  • In Majority-Plurality Two-Round elections any candidate who has received the votes of over 12.5 per cent of the registered electorate in the first round can stand in the second round. Whoever wins the highest numbers of votes in the second round is then declared elected, regardless of whether they have won an absolute majority or not.

• Majority-Runoff (Two-Round System)

  • The most common method for the second round of voting in a Two-Round System is a straight "run-off" contest between the two highest vote-winners from the first round.

Any system which consciously attempts to reduce the disparity between a party's share of the national vote and its share of the parliamentary seats.

• List Proportional Representation (List PR)

  • In its most simple form List PR involves each party presenting a list of candidates to the electorate, voters vote for a party, and parties receive seats in proportion to their overall share of the national vote. Winning candidates are taken from the lists.

• Single Transferable Vote (STV)

  • A preferential proportional representation system used in multi-member districts. To gain election, candidates must surpass a specified quota of first-preference votes. Voters' preferences are re-allocated to other continuing candidates when an unsuccessful candidate is excluded or if an elected candidate has a surplus.

• Party Block Vote (PB)

  • A form of the Block Vote in which electors choose between parties rather than candidates. The successful party will typically win every seat in the district.

Those electoral systems which provide, on average, results which fall some way in between the proportionality of PR systems and the direct-representation of plurality-majority systems.

• Mixed Member Proportional (MMP)

  • Systems in which a proportion of the parliament (usually half) is elected from plurality-majority districts, while the remaining members are chosen from PR lists. Under MMP the list PR seats compensate for any disproportionality produced by the district seat results.

• Open List

  • A form of List Proportional Representation in which electors can express a Parallel System - A semi-proportional system in which proportional representation is used in conjunction with a plurality-majority system but where, unlike MMP, the PR seats do not compensate for any disproportionality arising from elections to the plurality-majority seats.

• Single Non-Transferable Vote (SNTV)

  • A semi-proportional system which combines multimember districts with a First Past the Post method of vote counting, and in which electors have only one vote.