Proportional Representation

Family of electoral formulas that allocate legislative seats to parties in proportion to the share of the vote each receives, in contrast to the winner-take-all logic of a plurality system. Seats are distributed across multi-member constituencies, or in some systems a single nationwide constituency, using a formula such as the D'Hondt method, devised by the Belgian mathematician and jurist Victor D'Hondt and first described in 1878, or the Sainte-Lague method. Belgium became the first country to hold a national parliamentary election under proportional representation, on 27 May 1900, after the D'Hondt-based reform became law on 29 December 1899, replacing single-member constituencies with multi-member ones typically electing between three and eighteen members; that 1899 reform is the origin year this atlas records for the mechanism, a first national adoption rather than a first proposal. The system spread across continental Europe in the following decades and today underlies most legislatures of the European Union and much of Latin America. Because a proportional formula lets smaller parties win seats in rough proportion to their support rather than being shut out entirely, it tends toward multi-party legislatures in which no single party wins a majority outright, an effect formalized as Duverger's law and one directly reflected in proportional representation's well documented tendency to produce coalition government. The single transferable vote is one specific method of achieving proportionality, using ranked ballots in multi-member districts rather than party lists.