Mixed-member proportional representation, also termed mixed-member proportional voting and commonly abbreviated to MMP, is a voting system originally used to elect representatives to the German Bundestag, and which has now been adopted by numerous legislatures around the world.
MMP is similar to other forms of proportional representation (PR) in that the overall total of party members in the elected body is intended to mirror the overall proportion of votes received; it differs by including a set of members elected by geographic constituency who are deducted from the party totals so as to maintain overall proportionality. MMP is similar to the additional member system used in the United Kingdom, which has no overhang seats or balance seats and consequently is not perfectly proportional.
In Germany, where it is used on the federal level and on most state levels, MMP is known as personalized proportional representation. In Quebec, where an MMP model was studied in 2007, it is called the compensatory mixed-member voting system (système mixte avec compensation or SMAC).
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In most models the voter casts two votes: one for a constituency representative and one for a party. In the original variant used at first in Germany, still used by two States of Germany until 2010, both votes were combined into one, so that voting for a representative automatically means also voting for the representative's party. Most of Germany changed to the two-vote variant to make local MPs more personally accountable; the state of North Rhine-Westphalia finally made the change in 2010. Voters can vote for the local person they prefer for local MP without regard for party affiliation, since the partisan make-up of the legislature is determined only by the party vote. In the 2005 New Zealand election, 20% of local MPs were elected from electorates (constituencies) which gave a different party a plurality of votes.
In each constituency, the representative is chosen using a single winner method, typically first-past-the-post (that is, the candidate with the most votes, by plurality, wins).
Most systems used closed party lists to elect the non-constituency MPs (also called list MPs). Depending on the jurisdiction, candidates may stand for both a constituency and on a party list (referred to in New Zealand as dual candidacy), or may be restricted to contend either for a constituency or for a party list, but not both. If a candidate is on the party list, but wins a constituency seat, they do not receive two seats; they are instead crossed off the party list and replaced with the next candidate down.
In Bavaria the second vote is not simply for the party but for one of the candidates on the party's regional list: Bavaria uses seven regions for this purpose. A regional open-list method was also recommended for the United Kingdom by the Jenkins Commission (where the similar Additional Member System is used) and for Canada by the Law Commission of Canada.
In Baden-Württemberg there are no lists; they use the "best near-winner" method in a four-region model, where the regional members are the local candidates of the under-represented party in that region who received the most votes in their local constituency without being elected in it.
At the regional or national level (i.e. above the constituency level) several different calculation methods have been used, but the basic characteristic of the MMP is that the total number of seats in the assembly, including the single-member seats and not only the party-list ones, are allocated to parties proportionally to the number of votes the party received in the party portion of the ballot. This can be done by the largest remainder method or a highest averages method: either the D'Hondt method or the Sainte-Laguë method. Subtracted from each party's allocation is the number of constituency seats that party won, so that the additional seats are compensatory (top-up). If a party wins more FPTP seats than the proportional quota received by the party-list vote, these surplus seats become overhang seats to work towards restoring a full proportionality. In most German states, but not federally, "balance seats" are added to compensate for the overhang seats and achieve complete proportionality. In the last election in Scotland, the highest averages method resulted in a majority government for the Scottish National Party with only 44% of the party vote.
When a party wins more constituency seats than it would be entitled to from its proportion of (party list) votes, overhang seats can occur.
In Germany's Bundestag and the New Zealand House of Representatives, all these constituency members keep their seats. For example, in New Zealand's 2008 General Election the Māori Party won 2.4% of the Party Vote, which would entitle them to 3 seats in the House, but won 5 constituency seats, leaving an overhang of 2 seats, which resulted in a 122-member house. If the party vote for the Māori Party had been more in proportion with the constituency seats won, there would have been a normal 120-member house.
In most German states, the other parties receive extra seats ("balance seats") to create full proportionality. For example, the provincial parliament (Landtag) of North Rhine Westphalia has, instead of the usual 50% compensatory seats, only 29% unless more are needed to balance overhangs. If a party wins more local seats than its proportion of the total vote justifies, the size of the Landtag increases so that the total outcome is fully proportional to the votes, with other parties receiving additional list seats to achieve that.
As in numerous proportional systems, in order to be eligible for list seats in many MMP models, a party must earn at least a certain percentage of the total party vote, or no candidates will be elected from the party list. Candidates having won a constituency will still have won their seat. In New Zealand the threshold is 5%, in Bolivia 3%, in Germany 5% for elections for federal parliament and most state parliaments. A party can also be eligible for list seats if it wins at least three constituency seats in Germany, or at least one in New Zealand. Having a member with a 'safe' constituency seat is therefore a tremendous asset to a minor party in New Zealand.
MMP is currently in use in:
In March 2004 the Law Commission of Canada proposed a system of MMP, with only 33% of MPs elected from regional open lists, for the Canadian House of Commons but Parliament’s consideration of the Report in 2004-5 was stopped after the 2006 election.
In 2007 the Citizens' Assembly on Electoral Reform in Ontario, Canada, also recommended the use of MMP in future elections to the Legislative Assembly of Ontario, with a ballot similar to New Zealand's, and with the closed province-wide lists used in New Zealand but with only 30% compensatory members. A binding referendum on the proposal, held in conjunction with the provincial election on 10 October 2007, saw it defeated.
In systems with a threshold, tactical voting for a minor party that is predicted to poll close to or slightly below the threshold is relatively common. Some voters may be afraid the minor party will poll below the threshold, and that that would weaken the larger political camp to which the minor party belongs. For example the German moderate-right Free Democratic Party (FDP) has often received votes from voters who preferred the larger Christian Democratic Union (CDU) party, because they feared that if the FDP received less than 5% of the votes, the CDU would have no parliamentary allies and would be unable to form a government on its own. This tactical voting also ensures that less votes are wasted, but at the cost of giving the FDP more seats than CDU voters would ideally have preferred.
Similarly, in New Zealand, some voters who preferred a large party have voted for the minor party's local candidate to ensure it qualifies for list seats on the back of winning a single electorate. This notably occurred in the right-wing inner Auckland electorate of Epsom in 2008 and 2011, where the National Party voters gave their local vote to the ACT Party. In this case the tactic maintained some proportionality by bypassing the 5% threshold, but is largely disfavoured by the public due to it awarding smaller parties extra list seats while parties with a higher party vote percentage that don't win an electorate receive no seats (this occurred in 2008 when ACT was awarded 5 seats on the back of one electorate seat and 3.7% of the party vote, while New Zealand First with no electorate seats and 4.1% of the party vote were awarded none.) In August 2012, the initial report on a review of the MMP system by the Electoral Commission recommended abolishing the one electorate seat threshold, meaning a party winning an electorate seat but not crossing the 5% threshold (which the same report recommends lowering to 4%) is only awarded that electorate seat.
In terms of tactical voting, the vote for the constituency representative is normally much less important than the party vote in determining the overall result of an election; but in some cases a party may be so certain of winning seats in the constituency elections that it expects no extra seats in the proportional top-up. 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 those German states which add "balance seats"; since those states maintain full proportionality even when a party wins too many constituency seats. This tactic is less prevalent in good MMP models with enough extra seats; for instance in Germany and the German states, generally 50% of the seats are "list seats" leading to less opportunities for overhangs.
In the 2005 election the two main parties expected no extra seats, and encouraged voters to use their list votes for allied minor parties. This became so severe that it totally distorted the working of the model. The oddity was noted that only one local member was elected from parties receiving list seats. Though, the top two parties earned Rather than increase the number of "list seats" or allow additional "overhang" seats, Albania recently decided to change to a pure-list system.
Political parties can also abuse the system by splitting their party into two, if this is allowed by electoral law. One subdivision of the party contests the constituency seats, the other contests the list seats. This is significantly easier to manipulate where voters have the option of a separate vote in the nominal and list tier. This tactic will produce an overhang. The two linked parties can co-ordinate their campaign and work together within the legislature, while remaining legally separate entities. This can also give other advantages in areas such as party funding.
For instance in the Italian general election, 2001, one of the two main coalitions (the House of Freedoms, which opposed the scorporo system, (an alternate version of MMP), linked many of their constituency candidates to a decoy list (liste civetta) in the proportional parts, under the name Abolizione Scorporo. As a defensive move, the other coalition, Olive Tree, felt obliged to do the same, under the name Paese Nuovo. The constituency seats won by each coalition would not reduce the number of proportional seats they received. Between them, the two decoy lists won 360 of the 475 constituency seats, more than half of the total of 630 seats available, despite winning a combined total of less than 0.2% of the national proportional part of the vote. In the case of Forza Italia (part of the House of Freedoms), the tactic was so successful that it did not have enough candidates in the proportional part to receive as many seats as it in fact won, missing out on 12 seats.
In the 2007 Lesotho general election, the two leading parties, the Lesotho Congress for Democracy and the All Basotho Convention used decoy lists, respectively named the National Independent Party and the Lesotho Workers' Party to avoid the compensatory mechanisms of MMP. In the 2012 election, the voting system was adjusted to link the local and list seats to limit the decoy lists' effectiveness, resulting in a more proportionate election result.[unreliable source?]
Venezuela previously used MMP as its electoral system. The tactic was originated by the opposition governor of Yaracuy and subsequently adopted by pro-Chavez parties. After the decoy list tactic withstood a constitutional challenge, Venezuela eventually reverted to parallel voting.
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