Mixed system, two votes. One vote elects a constituency representative via FPTP in single-member seats. A second vote is for a regional/closed party list (Regional (Closed) List); regional list seats are allocated to “top up” parties that are under-represented from the constituency results alone so overall seat totals better match regional vote share.
Used for the Scottish Parliament and the Senedd (Welsh Parliament).
Disadvanages of AMS
Two classes of representative
- Constituency members have a clear local mandate; list members don’t
- Can create resentment/“second class MSP” perception, list members seen as less legitimate despite equal formal powers
Complexity
- Two votes, two counting methods, plus a top-up calculation — harder for voters to fully understand than a single FPTP vote
- Similar criticism to that levelled at STV
Not fully proportional
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Only “corrects” disproportionality up to the number of list seats available; a party that sweeps constituency seats can still end up over-represented overall
- e.g. SNP’s landslide of constituency seats in 2011 gave them an overall majority despite AMS being designed to prevent single-party majorities
Can encourage tactical list voting / “list-gaming”
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Parties can run affiliated “sister” list-only parties to win top-up seats their main party wouldn’t qualify for
- e.g. Alba Party’s 2021 strategy of urging SNP voters to give their list vote to Alba instead
Advantages of AMS
Balances local link with proportionality
- Retains FPTP’s constituency accountability for most seats
- Regional list corrects the worst of FPTP’s disproportionality, unlike pure FPTP (FPTP)
Reduces wasted votes
- List vote gives smaller parties a realistic route to representation even without a geographically concentrated base
- Softer version of the proportionality benefit claimed for STV and regional list systems
Discourages single-party dominance (usually)
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Top-up mechanism is explicitly designed to produce coalition/minority government as the norm, encouraging cross-party cooperation
- e.g. most Scottish Parliament and Senedd terms have produced coalition or minority governments
Voter choice between party and candidate
- Voters can split their ticket — vote for a preferred local candidate with one vote and a different preferred party with the other
- More flexibility than the single choice offered by FPTP or closed list