Mixed-member proportional representation
Mixed-member proportional representation (MMP or MMPR) is a mixed electoral system which combines local majoritarian elections with a compensatory tier of party list votes, which are used to allocate additional members in a way that aims to produce proportional representation overall. In most MMP systems, voters get two votes: one to decide the representative for their single-seat constituency, and one for a political party. Some countries use single vote variants of MMP, although this article focuses primarily on dual vote versions of MMP.
Not to be confused with Mixed-member majoritarian representation or Parallel voting.
Seats in the legislature are filled first by the successful constituency candidates, and second, by party candidates based on the percentage of nationwide or region-wide votes that each party received.[1][2][3] The constituency representatives are usually elected using first-past-the-post voting (FPTP). The nationwide or regional party representatives are, in most jurisdictions, drawn from published party lists, similar to party-list proportional representation. To gain a nationwide representative, parties may be required to achieve a minimum number of constituency seats, a minimum percentage of the nationwide party vote, or both.
MMP differs from parallel voting in that the nationwide seats are allocated to political parties in a compensatory manner in order to achieve proportional election results. Under MMP, two parties that each receive 25% of the votes end up with about 25% of the seats, even if one party wins more constituency seats than the other. Depending on the exact system implemented in a country and the results of a particular election, the proportionality of an election may vary.[4] Overhang seats may reduce the proportionality of the system, although this can be compensated for by allocating additional party list seats to cover any proportionality gap.[5]
MMP was first used to elect representatives to the German Bundestag, and has been adopted by New Zealand and others, with modifications.
Other names[edit]
In Germany, where it is used on the federal level and in most states, MMP is known as personalized proportional representation (German: personalisiertes Verhältniswahlrecht). This version of MMP produced very proportional election results by a number of additional compensatory seats, known as leveling seats. Germany recently modified their system to not allow overhang seats in a way that not all local districts are guaranteed to elect the plurality winner, thereby eliminating the need for leveling seats also: However due to this revision, the system is no longer considered to be MMP in the sense of a mixed member system combining proportional and majoritarian representation, but a personalized/localized version of PR. As it retains the individual candidate vote in a clearly distinct fashion from open-list systems, it may still be considered mixed-member proportional in the sense of a proportional system having two kinds of MP: one (may be) elected by personal (candidate) votes, one elected by (closed list) votes.
In the Canadian province of Quebec, where an MMP model was studied in 2007,[6] it is called the compensatory mixed-member voting system (système mixte avec compensation or SMAC). In the United Kingdom the semi-proportional implementation of MMP used in Scotland, Wales, and the London Assembly is referred to as the additional member system.[7][8]
Tactical manipulation[edit]
Split ticket voting[edit]
In other cases, a party may be so certain of winning a large number of constituency seats that it expects no extra seats in the proportional top-up (list seats). Some voters may therefore seek to achieve double representation by voting tactically for another party in the regional vote, as a vote for their preferred party in the regional vote would be wasted. This tactic is much less effective in MMP models with a relatively large share of list seats (50% in most German states, and 40% in the New Zealand House of Representatives) and/or ones which add "balancing seats", leading to fewer opportunities for overhangs and maintaining full proportionality, even when a party wins too many constituency seats.