British academy

Choosing an electoral system

A report by the British Academy Policy Centre, prepared by Professor Simon Hix, Professor Ron Johnston FBA and Professor Iain McLean FBA with research assistance from Angela Cummine 


Choosing an Electoral System (1.4MB pdf) identifies the characteristics of the variety of electoral systems used around the world, and discusses their implications for issues such as:

  • voter turn-out;
  • minority parties;
  • party politics;
  • proportionality;
  • and effective government.

Download the full report (1.4MB pdf)

In brief

What prior research shows

There is no deterministic relationship between the type of system and particular election outcomes (i.e. turnout level, likelihood of one party achieving a majority). There is also no perfect electoral system: any system used will involve a trade-off between the representativeness of Parliament and government accountability, and between the accountability of individual politicians and the cohesiveness of political parties.

Two key issues: Constituency magnitude and apportionment

The magnitude of constituencies (the number of MPs they elect) affects the quota a party wins and how many seats they get awarded – and has a crucial influence on election outcomes in virtually all electoral systems.

There are two parts to apportionment: the allocation of seats to a constituency and the allocation of seats to parties, based on their share of the vote. A number of different systems can be used for both.

Single-member constituency systems

These include First Past The Post (FPTP), Alternative Vote (AV) and Supplementary Vote (SV). None are likely to deliver a proportional outcome.

Multi-member constituency systems:

Closed-List PR, Open-List PR, and Single Transferable Vote

Of these, Closed-List and Open-List PR are often more proportional in outcome than STV. 

Open-List PR and STV elections have more of a focus on particular candidates and their accountability, so electors tend to prefer these systems, while party leaders like Closed-List PR.

Mixed systems with both single- and multi-member constituencies

Two main types of system have been introduced: Mixed Member Proportional/Additional Member Systems (MMP/AMS) and Mixed Member Majoritarian (MMM).

Both have two components: the election of territorial representatives from single-member constituencies (using FPTP or AV); and a List sytsem for one or more multi-member constituencies.

In MMP/AMS the List contest compensates for any disproportionality in the single-member contests, while in MMM the two sets of results are simply added together to produce an overall result.

Conclusions: The UK as an Electoral Laboratory

FPTP is traditionally strong in electing a representative for a segment of national territory, but evidence suggests that STV or Open-List PR could be equally so.

Proportional representation is more likely to be achieved under Closed- and Open-List multi-member systems, as well as under some versions of MMP/AMS.

Open-List and STV provide voters with greater preferential voting within a party. It is clearly difficult to achieve a balance on all three fronts.

It is worth noting that PR systems will not necessarily bring in coalition governments, nor, if it did would these be unstable by nature. However, changing an electoral system means that forms of campaigning and policy formulation must change too, to target voters in different ways.

The report was launched at the British Academy on 10 March 2010.

News release, 10 March 2010: 'Electoral systems under the microscope'

Article in British Academy Review: 'How to Choose an Electoral System', by Simon Hix, Ron Johnston and Iain McLean (pdf)