Additional member system

Additional member system. The additional member system is a mixed electoral system that combines elements of first-past-the-post voting with proportional representation. Voters typically cast two ballots: one for a local constituency representative and a second for a political party list. This system is used in national elections in countries like Germany, New Zealand, and Scotland, aiming to balance direct local accountability with broader proportional outcomes in the legislative body.

Overview

The system originated from post-war reforms in West Germany, where it is known as mixed-member proportional representation. It was designed to stabilize the Weimar Republic's fragmented party system while ensuring geographic representation. Key political scientists like Maurice Duverger and Arend Lijphart have analyzed its impact on party systems and governance. The adoption of this model has influenced electoral engineering in nations emerging from conflict, such as in the constitutions of South Africa and Iraq.

How the system works

In a typical election, such as for the Scottish Parliament, each voter receives two ballots. The first is for a constituency Member of the Scottish Parliament elected via first-past-the-post in districts like Glasgow Kelvin or Edinburgh Central. The second ballot is for a regional party list, covering larger areas like Lothian or Highlands and Islands. Seats are allocated from these lists to correct disproportionality from the constituency results, often using a formula like the Sainte-Laguë method or the d'Hondt method. The German Bundestag employs a similar process, with its Federal Returning Officer overseeing seat allocation to ensure the overall composition reflects the party list vote share.

Variations and examples

The primary variation is between mixed-member proportional, used in Germany and New Zealand, and the mixed-member majoritarian system, used in Japan and the London Assembly. In Wales, the Senedd uses a model where regional members are elected from closed lists. The Italian Parliament experimented with a version known as the Mattarellum law in the 1990s. Other implementations include elections for the Bolivian Congress and the Lesotho National Assembly, each with unique thresholds and compensatory mechanisms.

Advantages and disadvantages

Proponents, such as the Electoral Reform Society, argue it provides fairer representation for parties like the Green Party of England and Wales and the Liberal Democrats, while maintaining a link between constituents and their Member of Parliament. Critics, including scholars like Giovanni Sartori, contend it can create two classes of legislators and strengthen party control via closed list selections. The system can also lead to overhang seats, a recurring issue in the German Bundestag, and may not fully eliminate strategic voting, as seen in elections for the New Zealand House of Representatives.

Comparison with other electoral systems

Compared to single transferable vote systems used in Ireland and Malta, it typically offers less intra-party choice but simpler ballots. Against pure party-list proportional representation systems found in Israel or the Netherlands, it provides stronger geographic ties. When contrasted with the alternative vote used for the Australian House of Representatives, it generally yields more proportional outcomes but can reduce local majority support. The system's hybrid nature is often studied alongside the parallel voting model of Mexico and the dual-member proportional proposal in Canada.

Category:Electoral systems