Proportional representation

Proportional representation (PR) is achieved by any electoral system under which subgroups of an electorate are reflected proportionately in the elected body. The party make-up of the elected representatives reflects the party make-up of the votes cast. The concept applies to representation of political parties and also other divisions of voters.

The term is used for any of the various electoral systems that produce proportional representation. The aim of such systems is that all votes cast, or at least a large proportion, are used to elect someone and that each representative in an assembly is elected by a roughly equal number of votes, and thus all (or most) votes have equal weight. Under other election systems, a slight majority in a district – or even just a minority of votes when it forms a plurality – is all that is needed to elect a member or group of members. PR systems provide balanced representation to different factions, usually defined by parties, reflecting how votes were cast.

In PR systems where only a choice of parties is allowed, the seats are allocated to parties in proportion to the vote tally or vote share each party receives. Under open-list PR and single transferable voting, the winning candidates are elected both on personal appeal and party label.

Exact proportionality is never achieved under PR systems, except by chance. The use of electoral thresholds that are intended to limit the representation of small, often extreme parties reduces proportionality in list systems, and any insufficiency in the number of levelling seats reduces proportionality in mixed-member proportional (MMP) or additional-member systems. Under single-transferable-vote (STV) or party-list PR systems, districts with a small or moderate number of seats allow local representation but may reduce proportionality. Any use of districts dividing the electorate creates a possibility of somewhat disproportionate results. Other sources of disproportionality arise from electoral tactics, such as party splitting in some MMP systems, where the voters' true intent is difficult to determine.

Nonetheless, PR systems approximate proportionality much better than single-member plurality voting (SMP) and block voting. PR systems also are more resistant to gerrymandering and other forms of manipulation.

Some PR systems do not necessitate the use of parties; others do. The most widely used families of PR electoral systems are party-list PR, used in 85 countries; mixed-member PR (MMP), used in 7 countries; and single transferable vote (STV), used in Ireland, Malta, the Australian Senate, and the Indian Rajya Sabha. Proportional representation systems are used at all levels of government and are also used for elections to non-governmental bodies, such as corporate boards.