Proportional Systems: AMS, STV, Regional List

This lesson examines the proportional and hybrid electoral systems used in parts of the UK and their key features, advantages, and disadvantages.

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Why Study Proportional Systems?

Although FPTP is used for UK general elections, several other systems are used across the UK:

System	Where Used
Additional Member System (AMS)	Scottish Parliament, Welsh Senedd, London Assembly
Single Transferable Vote (STV)	Northern Ireland Assembly, Scottish local elections
Regional List	Former European Parliament elections
Supplementary Vote (SV)	Was used for London mayoral elections (now FPTP)

Understanding these systems is essential for comparing approaches to representation and evaluating proposals for reform.

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Additional Member System (AMS)

AMS is a hybrid system that combines FPTP with a proportional element.

How It Works

1. Each voter has two votes:
   • First vote: for a constituency candidate (elected by FPTP)
   • Second vote: for a party list (regional/list seats allocated proportionally)
2. The list seats are allocated to compensate for the disproportionality of the constituency results
3. This produces a more proportional overall result than FPTP alone

Example: The Scottish Parliament

• 73 constituency MSPs elected by FPTP
• 56 regional (list) MSPs elected proportionally from 8 regions (7 per region)
• Total: 129 MSPs

Advantages of AMS

Advantage	Explanation
More proportional	The list element compensates for FPTP's distortions
Constituency link	Voters still have a local constituency representative
Voter choice	Two votes allow voters to split their support (e.g. constituency vote for one party, list vote for another)
Smaller party representation	Smaller parties can win list seats even if they struggle in constituencies (e.g. the Greens in Scotland)

Disadvantages of AMS

Disadvantage	Explanation
Two classes of representative	Constituency MSPs and list MSPs may have different mandates and workloads
Complexity	More complex than FPTP for voters to understand
Coalition government	Less likely to produce single-party majorities — coalitions or minority governments are common
Party control of lists	Party leaders choose the order of candidates on the list, reducing voter choice

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Single Transferable Vote (STV)

STV is a proportional system that uses multi-member constituencies and a preferential ballot.

How It Works

1. Voters rank candidates in order of preference (1, 2, 3, etc.)
2. To win a seat, a candidate must reach a quota (calculated using the Droop formula: $\text{quota} = \frac{\text{total votes}}{\text{seats} + 1} + 1$quota=seats+1total votes​+1)
3. If a candidate exceeds the quota, their surplus votes are redistributed to voters' next preferences
4. If no candidate reaches the quota, the bottom candidate is eliminated and their votes are redistributed
5. This process continues until all seats are filled

Where STV Is Used

• Northern Ireland Assembly (6-member constituencies)
• Scottish local elections (3–4 member wards)
• Republic of Ireland (general elections)

Advantages of STV

Advantage	Explanation
Proportional outcomes	Results closely reflect the distribution of voter preferences
Voter choice	Voters choose between individual candidates, not just parties — they can rank candidates from the same party
Fewer wasted votes	Most votes contribute to electing a representative through the transfer mechanism
Multi-member constituencies	Voters have multiple representatives to contact, potentially improving representation

Disadvantages of STV