First Past the Post vs Proportional Representation: What Each System Rewards

Arguments about electoral reform tend to be conducted as though one system is fair and the other is not. The more useful framing is that every system optimises for something at the expense of something else, and the choice is about which trade-off a country prefers to live with.

How first past the post behaves

Under first past the post, the country is divided into single-member constituencies and the candidate with the most votes in each wins the seat. No majority is required. The system is simple to administer, produces an unambiguous local representative, and is easy for voters to understand.

Its central characteristic is that it converts a plurality of votes into a much larger share of seats. A party with forty per cent of the national vote, efficiently distributed, can win a comfortable parliamentary majority. The corollary is that support which is geographically spread but nowhere concentrated translates into very few seats — which is why parties with substantial national vote shares can end up with a handful of representatives while regionally concentrated parties with far fewer votes do considerably better.

Political scientists describe the tendency of such systems towards two dominant parties as Duverger’s law. The mechanism has two parts: mechanical, in that small parties are penalised in seat allocation, and psychological, in that voters anticipating this penalty avoid wasting votes on candidates who cannot win locally.

How proportional systems behave

Proportional representation covers a family of systems rather than one. Party list systems allocate seats in multi-member districts in proportion to vote share, either from a closed list controlled by the party or an open list where voters influence which candidates are elected. The single transferable vote uses ranked ballots in multi-member constituencies, allowing voters to discriminate between candidates of the same party. Mixed member proportional combines constituency seats with a compensatory list that corrects the overall result towards proportionality.

The defining feature is that seat share tracks vote share closely. Smaller parties win representation roughly in line with their support, which raises the number of parties in the legislature and, in most cases, makes single-party majorities rare.

The government formation trade-off

This is where the real difference lies. Majoritarian systems typically produce single-party governments with clear mandates and equally clear accountability: voters know who to reward or punish. The cost is that a government supported by a minority of voters can implement its full programme, and that alternation can be abrupt.

Proportional systems typically produce coalitions. Policy emerges from post-election negotiation, which means the governing programme is not any single party’s manifesto and voters cannot straightforwardly assign credit or blame. Supporters argue this produces more consensual, stable policy over time. Critics argue it hands disproportionate influence to small parties whose votes are needed to form a majority, and moves the real decisions behind closed doors.

Thresholds and their effects

Most proportional systems include a threshold — commonly between three and five per cent — below which a party wins no list seats. Thresholds exist to prevent fragmentation, and they work, but they reintroduce a version of the wasted vote problem. A threshold set too high excludes meaningful blocs of opinion; set too low it can produce legislatures with a dozen or more parties and correspondingly difficult coalition arithmetic.

The constituency link

One argument for majoritarian systems that survives most scrutiny is the constituency link. Each area has one identifiable representative with an incentive to attend to local concerns, and voters have a clear person to contact. Pure list systems weaken this considerably. Mixed and single transferable vote systems are explicit attempts to retain a geographic link while improving proportionality, and they largely succeed, at the cost of greater complexity.

What the comparative evidence suggests

Cross-national research finds proportional systems associated with higher turnout, more women and minority representatives in legislatures, and somewhat higher public spending as a share of output. Majoritarian systems are associated with more decisive policy change and clearer accountability for outcomes. Claims that either system produces better economic performance overall do not hold up well once other factors are controlled for.

Perhaps the most important finding is that electoral system effects are conditional on other institutions. The same system behaves differently in a country with strong regional identities than in one without, and differently again depending on whether the legislature faces a directly elected executive.

The practical question

Reform debates usually founder on the fact that the party best placed to legislate change is, by definition, the party the current system has just advantaged. That asymmetry — rather than any argument about fairness — explains most of why electoral systems change so rarely, and why when they do it is usually following a crisis of legitimacy rather than a considered comparison of trade-offs.