What is the Additional Member System (AMS)?
The Additional Member System, or AMS, is a mixed electoral system. This means that it combines First Past the Post (FPTP) voting for single-member constituencies with proportional voting via party lists, in order to make the number of seats won by each political party more closely match the number of votes they received.
The aim of this electoral system is to achieve a more proportional parliament, while retaining direct representation from local members of parliament.
What elections use AMS?
In the UK, elections to the Scottish Parliament and Welsh Senedd use the Additional Member System to elect its representatives, as does the London Assembly.
Internationally, Germany and New Zealand are well-known examples that use this voting system in their general elections. Most state elections in Germany also use it, and New Zealand has been electing representatives in this way since 1994, following a referendum the year before.
Outside of the UK, AMS is known as Mixed-Member Proportional (MMP) representation.
How do I vote under AMS?
For elections using AMS, voters are given a ballot paper and asked to record two votes by putting a cross (‘X’) inside the box next to the name of their preferred candidate and party.
On the left-hand side of the ballot paper, voters select one candidate to represent their constituency as the local Member of Parliament (MP). Just like in UK general elections, voters can only vote for one candidate and the candidate with the most votes wins. This is known as First Past the Post (FPTP).
On the right-hand side, voters can vote for their preferred party to represent them at a regional level. Each party provides a list of regional candidates in advance of the election and a vote for the party is a vote to make more of their list of candidates into regional MPs.
Counting the votes
The constituency votes are counted first and the candidate with the most votes is elected as the representative. The winning candidate only has to win one more vote than their leading opponent, and therefore does not have to win a majority of votes. This is known as a plurality.
Once all of the constituencies have been decided, ‘additional members’ are allocated by counting the second votes for the regional party lists. By taking into account how many seats a party won in the first set of votes, ‘additional members’ are added to make the overall election results fairer and more proportional, according to how the people voted.
Advantages
More proportional / representative: Most importantly, the overall result of an AMS election is that parties win a number of seats that better reflects the number of votes they won.
Every vote counts: In a FPTP election, third-party voters often have to vote tactically to have a better chance of a preferred candidate winning a seat. Whilst this is still the case for their first vote in an AMS election, voters may vote for the party of their choice in the second, party list vote, as these are elected proportionally, and every vote increases their chance of election. Voting for a different party in the list vote is known as ‘split-ticket’ voting.
Political diversity: Parties that have significant support across the country yet have little chance of gaining representation via a FPTP election, are able to win a fair number of seats via the party list vote, which better reflects their level of support. This increases political diversity in parliament. Since parties also have an equal chance of winning across the country via the party list vote, no region can be neglected during campaigning, which cannot be said for ‘safe’ constituency seats that rarely change hands.
Greater representation: In FPTP, a winning candidate does not need to achieve a majority, so the majority of voters will be represented by an MP who may not share their views. However, party list MPs provide a second layer of representation and constituents may approach one of their regional MPs for support.
Disadvantages
Public misconceptions: A common misconception is that voters think AMS is a preferential voting system and are voting for their first and second choice candidates. This is not the case; you are voting for a candidate and a party and these may be the same for both votes.
Majority government less likely: AMS elections mean that coalitions or minority governments are more likely to occur, resulting in compromise politics, as it is difficult for one party to form a majority and gain overall control. However, majority government is still possible, as happened in Scotland in 2011 and New Zealand in 2020.
Two classes of MPs: As some members of parliament represent a constituency, they will receive local casework, whereas party list representatives will not. This can create tension regarding specific MP’s roles.
A compromise solution: As AMS systems have a fixed number of party list MPs elected to parliament, this is not always enough to make up for the lack of proportionality in the constituency results.
Parties control regional lists: In UK elections using AMS, regional party lists are ‘closed’. This means that political parties control the order in which additional members are elected, as opposed to voters.
