Proportional representation

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Proportional representation (PR) refers to any type of electoral system under which subgroups of an electorate are reflected proportionately in the elected body.^[1] The concept applies mainly to political divisions (political parties) among voters. The essence of such systems is that all votes cast – or almost all votes cast – contribute to the result and are effectively used to help elect someone. Under other election systems, a bare plurality or a scant majority are all that are used to elect candidates. PR systems provide balanced representation to different factions, reflecting how votes are cast.

In the context of voting systems, PR means that each representative in an assembly is elected by a roughly equal number of voters. In the common case of electoral systems that only allow a choice of parties, the seats are allocated in proportion to the vote tally or vote share each party receives.

The term proportional representation may be used to mean fair representation by population as applied to states, regions, etc. However, representation being proportional with respect solely to population size is not considered to make an electoral system "proportional" the way the term is usually used. For example, the US House of Representatives has 435 members, who each represent a roughly equal number of people; each state is allocated a number of members in accordance with its population size (aside from a minimum single seat that even the smallest state receives), thus producing equal representation by population. But members of the House are elected in single-member districts generally through first-past-the-post elections: a single-winner contest does not produce proportional representation as it has only one winner. Conversely, the representation achieved under PR electoral systems is typically proportional to a district's population size (seats per set amount of population), votes cast (votes per winner), and party vote share (in party-based systems such as party-list PR). The European Parliament gives each member state a number of seats roughly based on its population size (see degressive proportionality) and in each member state, the election must also be held using a PR system (with proportional results based on vote share).

The most widely used families of PR electoral systems are party-list PR, used in 85 countries;^[2] mixed-member PR (MMP), used in 7 countries;^[3] and the single transferable vote (STV), used in Ireland,^[4] Malta, the Australian Senate, and Indian Rajya Sabha.^[5][6] Proportional representation systems are used at all levels of government and are also used for elections to non-governmental bodies, such as corporate boards.

All PR systems require multi-member election contests, meaning votes are pooled to elect multiple representatives at once. Pooling may be done in various multi-member voting districts (in STV and most list-PR systems) or in single countrywide – a so called at-large – district (in only a few list-PR systems). A country-wide pooling of votes to elect more than a hundred members is used in Angola, for example. Where PR is desired at the municipal level, a city-wide at-large districting is sometimes used, to allow as large a district magnitude as possible.

For large districts, party-list PR is often used, but even when list PR is used, districts sometimes contain fewer than 40 or 50 members.^[7] STV, a candidate-based PR system, has only rarely been used to elect more than 21 in a single contest.^[a] Some PR systems use at-large pooling or regional pooling in conjunction with single-member districts (such as the New Zealand MMP and the Scottish additional member system). Other PR systems use at-large pooling in conjunction with multi-member districts (Scandinavian countries).

Pooling is used to allocate leveling seats (top-up) to compensate for the disproportional results produced in single-member districts using FPTP or to increase the fairness produced in multi-member districts using list PR. PR systems that achieve the highest levels of proportionality tend to use as general pooling as possible (typically country-wide) or districts with large numbers of seats.

Due to various factors, perfect proportionality is rarely achieved under PR systems. The use of electoral thresholds (in list PR or MMP), small districts with few seats in each (in STV or list PR), or the absence or insufficient number of leveling seats (in list PR, MMP or AMS) may produce disproportionality. Other sources are electoral tactics that may be used in certain systems, such as party splitting in some MMP systems. Nonetheless, PR systems approximate proportionality much better than other systems^[8] and are more resistant to gerrymandering and other forms of manipulation.

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