What is "proportional representation"

n. A voting principle aimed at securing a close match between the percentage of votes that groups of candidates (usually political party) obtain in elections, and the percentage of seat they receive in the elected body.

n. representation of all parties in proportion to their popular vote

Proportional representation (PR) characterizes electoral systems by which divisions in an electorate are reflected proportionately in the elected body. If 30% of the electorate support a particular political party, then roughly 30% of seats will be won by that party. The essence of such systems is that all votes contribute to the result: not just a plurality, or a bare majority, of them. Proportional representation requires the use of multiple-member voting districts (also called super-districts); it is not possible using single-member districts alone.

There are two PR voting systems: party list PR and the single transferable vote (STV). Mixed member proportional representation (MMP), also known as the Additional Member System, is a hybrid Mixed Electoral System that uses party list PR as its proportional component. MMP has the potential to be proportional or semi-proportional depending on a number of factors such as the ratio of FPTP seats to PR seats, the existence or nonexistence of compensatory seats to make up for overhang seats, and election thresholds.

With party list PR, political parties define candidate lists and voters vote for a list. The relative vote for each list determines how many candidates from each list are actually elected. Lists can be " closed" or " open"; open lists allow voters to indicate individual candidate preferences and vote for independent candidates. Voting districts can be small (as few as two in Chile) or as large as a province or an entire nation.

The single transferable vote uses small districts, with voters ranking individual candidates in order of preference. During the count, as candidates are elected or eliminated, surplus or discarded votes that would otherwise be wasted are transferred to other candidates according to the preferences. STV enables voters to vote across party lines and to elect independent candidates.

Mixed member proportional representation (MMP), also called the additional member system (AMS), is a hybrid, two-tier, mixed member system combining a non-proportional Plurality/Majoritarian election and a compensatory regional or national party list PR one. Voters have two votes, one for their single-member district and one for the party list, the party list vote determining the balance of the parties in the elected body. Biproportional apportionment, first used in Zurich in 2006, is a two-tier method for adjusting an election's result to achieve overall proportionality.

Some form of proportional representation is used for national lower house elections in 94 countries, party list PR being the most widely used (85). MMP is used in seven lower houses, and STV, despite long being advocated by political scientists, is used in only two: Ireland, since independence in 1922, and Malta, since 1921; in the United States, party bosses were generally opposed to it because it transferred more power to the electorate when selecting independent candidates to put forward.

As with all electoral systems, there are overlapping and contentious claims in terms of its advantages and disadvantages.