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 concept applies mainly to political divisions (political parties) among voters.

The term is also used for any of the various electoral systems that produce proportional representation. The aim of such systems is that all votes cast contribute to the result so that each representative in an assembly is mandated by a roughly equal number of voters, and therefore all votes have equal weight. Under other election systems, a slight majority in a district – or even simply 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. 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.

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, small districts with few seats in each allow local representation but may reduce proportionality. 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.