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Proportional representation (PR) is an electoral system in which divisions in an electorate are reflected proportionately in the legislature. 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.〔(【引用サイトリンク】url=http://www.fairvote.org/reforms/fair-representation-voting/ )〕 There are two generally accepted PR voting types: party list PR and the single transferable vote (STV).〔(【引用サイトリンク】url=http://aceproject.org/ace-en/topics/es/esd/esd02/default )〕 Mixed member proportional representation (MMP), a hybrid method that uses party list PR as its proportional component, and FPTP as its plurality component is considered a mixed electoral system, which is a middle ground between PR voting systems and Plurality voting systems.〔(【引用サイトリンク】url=http://www.electoral-reform.org.uk/voting-systems )〕〔(【引用サイトリンク】url=http://aceproject.org/ace-en/topics/es/esd/esd03/default )〕〔(【引用サイトリンク】url=http://www.ifes.org/publications/electoral-systems-and-delimitation-constituencies )〕 MMP has the potential to be proportional, however the results of MMP are almost always semi-proportional. This has led to some disagreement among scholars as to its classification.〔(【引用サイトリンク】url=http://www.ifes.org/publications/electoral-systems-and-delimitation-constituencies )〕 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", "open", or local; open lists allow voters to indicate individual candidate preferences and vote for independent candidates. Voting districts can be as large as a province or an entire nation. The single transferable vote uses smaller 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,〔 system combining a non-proportional single-winner 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.〔 A further system produces near perfect proportionality by dispensing with voting altogether: the random selection of representatives from the populace, known as sortition. It was used in ancient Athens and the Venetian Republic and is still used today in the summons to jury duty. In recent years, it has received increasing academic attention. Some form of proportional representation is used for national lower house elections in 94 countries, party list PR being the most widely used (85).〔(【引用サイトリンク】title=Electoral Systems Comparative Data, Table by Country )〕 MMP is used in seven lower houses, and STV 〔 is used in only two: Ireland, since independence in 1922, and Malta, since 1921. As with all electoral systems, there are overlapping and contentious claims in terms of its advantages and disadvantages.〔 ==PR systems in the broader family of voting systems== Most experts group electoral systems into 3 general categories: * PR systems; * mixed member systems; and * plurality/majority or single-winner systems;〔(【引用サイトリンク】url=http://www.electoral-reform.org.uk/voting-systems )〕〔(【引用サイトリンク】url=http://www.electoral-reform.org.uk/voting-systems )〕〔(【引用サイトリンク】url=http://aceproject.org/ace-en/topics/es/esd/esd03/default )〕〔(【引用サイトリンク】url=http://www.ifes.org/publications/electoral-systems-and-delimitation-constituencies )〕〔(【引用サイトリンク】title=The Systems and Their Consequences )〕 Discussions about PR often include comparisons between PR and plurality/majority voting systems, comparisons between PR and mixed systems, and among different types of PR systems. Party list PR and STV are considered to be the only two PR systems. Mixed member systems include MMP and MMM, also known as parallel voting.〔〔 The extent to which mixed member systems yield proportional results depends upon the features of each system, but MMP has the potential to be proportional due to the compensatory way that list seats are distributed like other a mixed systems. However, the ratio of FPTP seats to PR seats, the quantify of overhang seats, and the threshold needed to acquire PR seats are contributing factors as to why MMP produces semi-proportional results.〔〔〔〔〔http://www.eleccion2012mexico.com/project-definition〕〔(【引用サイトリンク】url=http://www.britannica.com/EBchecked/topic/479181/proportional-representation/ )〕 MMM adds an element of proportionality to single-winner systems by the addition of list seats, but distributes only the list seats proportionately without compensating for disproportions in the distribution of single-winner seats. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「proportional representation」の詳細全文を読む スポンサード リンク
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