The Additional Member System (AMS) is a branch of voting systems in which some
representatives are elected from geographic constituencies and others are elected under proportional representation from party lists. Voters have two votes, one for the party and the second for the
candidate in a constituency. The constituency representatives are generally elected under the first-past-the-post voting system. The party list representatives are elected by a second vote,
where the electors vote for a political party, not directly for an individual. The particular individuals selected come from
lists drawn up by the political parties before the election, at a national or regional level.
Variations of the AMS have different ways of determining how many party list representatives each party is entitled to. The
main difference between systems is whether the constituency representatives are counted when list representatives are allocated
to each party.
- Under the Mixed Member Proportional (MMP) or
Top-Up system, the aim is either for the party's total number of representatives, including constituency representatives,
to be proportional to its percentage of the party vote, or for the allocation of additional party list seats to offset some or
all of the disproportionate result in the constituencies. The party-list vote largely determines the number of representatives
the party has in the assembly.
- Under the Parallel Voting or Supplementary Member (SUP) system, the
party list seats are allocated proportionally within themselves, so any constituency seats the party may have won are
additional.
- Under the French proportional system designed to produce a strong majority, half the seats are given
proportionally between party lists and the other half given to the list with a plurality, thus ensuring that a single list wins
well over half the seats.
Parallel Voting is the most common variation among voting systems of the
world. Small parties will generally win more seats under MMP than SUP unless there is a threshold of
exclusion, such as the 5% or 3 constituencies threshold in Germany, or the 5% or 1 constituency seat threshold in New
Zealand.
Criticisms
Since the majority party and its coalition partners in an election are likely to win a large number of proportional seats,
additional member systems hand additional political power to the leader of government at the expense of regional directly elected
representatives. "List" candidates may become figureheads for the party leadership. While minority parties gain seats under
additional member systems, majority parties may lose diversity, leading to power concentrating in the hands of fewer individuals
than under a Plurality voting system.
See also
References
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