Mixed Member Proportional

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Mixed member proportional representation, also termed mixed-member proportional representation and commonly abbreviated to MMP, is a voting system used to elect representatives to numerous legislatures around the world. MMP is similar to other forms of proportional representation 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. In the United Kingdom, the form of MMP in use for several bodies is known as the additional member system (AMS), although the term additional member system can also be more broadly applied to include parallel voting, a non-proportional system.

Contents

Advantages

  • A large proportion of members are as individuals from single districts so voters still have someone rooting for their patch
  • Under most conditions it will produce just as proportional result as any other PR system

Disadvantages

  • If big parties gain more than their share in the single districts alone then there will not be enough top-up seats to make the result proportional unless the number of members to be elected is increased.
  • Big parties can abuse the system by running fake or decoy parties that allow them to scoop up top-up seats that they would not be entitled to unless there are safeguards.

Employment

MMP is currently in use in:

Hungary has a complex voting system that results in a less proportional representation than MMP but more proportional than Parallel voting.

Proposals for British elections

In 1976, the Hansard Society recommended that MMP be used for UK parliamentary elections, but instead of using closed party lists, it proposed that seats be filled by defeated candidates, on a 'best loser' basis. A similar system was proposed by the Independent Commission in 1999, known as Alternative Vote plus (AV+). This would involve the use of the Alternative Vote for electing members from single-member constituencies, and regional party lists. However, contrary to the Labour party's earlier manifesto promises, there was not a referendum before the 2001 election and the statement was not repeated.

Procedures

The voter makes two votes: one for a constituency representative and one for a party. In a lesser-used variant, which is used by some of the several States of Germany, both votes are combined into one, so that voting for a representative automatically means also voting for the representative's party.

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).

On the district or national level (i.e. above the constituency level) two different methods are used:

  • The total number of seats in the assembly are allocated to parties proportionally to the number of votes the party received in the party portion of the ballot. Subtracted from each party's allocation is the number of constituency seats that party won. The number of seats remaining allocated to that party are filled using the party's list.
  • Alternatively, something like a highest averages method is used to allocate the list seats, but the number of seats already won in the constituencies is taken into account in setting the denominators used in the calculations for the list seats.

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.

Overhang seats

Because a party can gain fewer seats by the party vote than needed to justify the won constituency seats, overhang seats can occur. There are different ways of dealing with overhang seats. In Germany's Bundestag and the New Zealand House of Representatives the overhang seats remain. In some systems the other parties receive extra seats to restore proportionality. In both cases the total number of seats raises. In the British cases (Scottish Parliament, Welsh Assembly, London Assembly), overhang seats are compensated by giving fewer seats to the other parties: the total number of sets remains the same, but at the expense of the other parties.

For example, in New Zealand's 2005 General Election the Māori Party won 2.1% of the Party Vote, entitling them to 3 seats in the House, but won 4 electorates, leaving an overhang of 1 seat, which results in a 121-member house.

Threshold

In order to be eligible for list seats in the New Zealand, German and various United Kingdom systems, a party must either earn at least 5% of the total party vote or must win at least one constituency seat (three constituency seats in Germany). If neither of the two conditions are met, no candidates from the party list are chosen. Candidates having won a constituency will still have won their seat. Having a member with a 'safe' constituency seat is therefore a tremendous asset to a minor party in such a system.

Potential for tactical voting

In terms of tactical voting, the first vote for the district representative is often much less important (than the second party list vote) in determining the overall result of an election; in other cases a party may be so certain of winning seats in the district election that it expects no extra seats in the proportional top-up. Some voters may therefore seek to get a double representation by voting tactically and splitting their votes, though this runs the risk of unintended consequences.

In systems with a threshold, tactical voting for a minor party that is predicted to poll slightly below the threshold is relatively common, especially by voters who are afraid that the minor party missing the threshold would weaken the larger political camp that the minor party belongs to. 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 five percent of the votes, the conservative camp would be weakened so much that the CDU wouldn't be able to form a government.

Decoy lists

Political parties can also abuse the system. They can separate their party in two. One contests the electorates seats, the other contests for the list seats. This will produce an overhang. They 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 2001 Italian elections, the two main coalitions (the House of Freedoms and the Olive Tree) linked many of their constituency candidates to decoy lists (liste civetta) in the proportional parts, under the names Abolizione Scorporo and Paese Nuovo respectively, so that if they won constituencies then they would not reduce the number of proportional seats received by the coalitions. Between them, the two decoy lists won 360 of the 475 constituency seats, more than half of the 630 total number of seats, 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.

Decoy lists are not used in most countries using MMP, where most voters vote for candidates from parties with long-standing names.

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