Proportional representation

An electoral system determines how votes are converted into seats. Under proportional representation, the goal is for a party that receives a given share of the vote to win a broadly corresponding share of seats in a legislature. This contrasts with plurality systems, in which a single winner may take a district's seat even without receiving a majority of its votes. PR is not one fixed formula: countries choose different rules to balance party representation, local links between representatives and voters, and the simplicity of the ballot and count.

In party-list PR, parties or other groups present candidate lists, and seats are allocated among lists according to their vote totals. Depending on the rules, voters may choose only a list or may also influence which candidates on a list are elected. Open-list arrangements give voters some say over candidate order, while closed lists leave more of that decision to the party. In the single transferable vote (STV), voters rank individual candidates in multi-seat districts; candidates who reach a quota are elected, and surplus or transferred preferences help fill the remaining seats. Mixed-member proportional (MMP) systems combine local constituency contests with party-list seats that adjust the overall result toward proportionality. These are distinct designs within a wider range of electoral arrangements.

A PR system's design affects how closely seats match vote shares. District magnitude—the number of seats elected in a district—is important: larger multi-member districts generally make it easier for parties with smaller vote shares to gain representation. Legal thresholds can prevent a party from receiving seats unless it reaches a minimum share of votes, while the formula used to allocate seats also affects the final totals. Some systems use one national district; others combine local districts with compensatory seats. As a result, two systems both described as proportional can produce different outcomes.

Supporters value PR because it can translate a wider range of voter preferences into legislative representation and reduce the gap between a party's vote share and seat share. Some designs also let voters choose among candidates while retaining a proportional result. Critics point to possible fragmentation of the party system, more complex coalition bargaining and rules that can be harder for voters or election administrators to understand. These are possibilities, not inevitable effects: thresholds, district size, party organization and other political conditions influence how a particular system works. Electoral-system design therefore involves choices among competing goals rather than a single arrangement that is best for every country.

New Zealand illustrates how a mixed-member proportional system works. Voters cast two ballots: a party vote and an electorate vote for a local candidate. The party vote largely determines each party's total share of seats; electorate winners take their seats, and party-list candidates fill the remaining places. A party normally needs at least 5 per cent of the party vote or to win an electorate seat to enter Parliament. This example shows how a system can combine local representation with an effort to make the legislature's overall party balance reflect voters' choices.