Parallel voting

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Parallel voting is a type of mixed electoral system in which representatives are voted into a single chamber using two or more different systems, most often first-past-the-post voting (FPTP) with party-list proportional representation (PR).^[1] It is the most common form of mixed member majoritarian representation (MMM), which is why these terms are often used synonymously with each other. In some countries, parallel voting is known as the supplementary member (SM) system, while in academic literature it is sometimes called the superposition method within mixed systems.

Parallel voting, as a form of mixed member majoritarian (semi-proportional) representation, is used in the election of national parliaments as well as local governments in various places such as Italy, Japan, Taiwan, Lithuania, Russia, and Argentina. It is distinct from the mixed election system known as mixed-member proportional representation (MMP) or the additional member system (AMS). Under MMP/AMS, district seats are filled and the party vote determines what proportional share of seats each party will receive in the legislature, through "topping up" the party's district seats. Under parallel voting, the election of the two groups of members are not connected in any way, except that they will serve in the same chamber.

While FPTP with PR is the most common pairing in parallel voting, many other combinations are possible. The proportion of list seats compared to total seats ranges widely; for example 30% in Taiwan, 37.5% in Japan and 68.7% in Armenia.^[2]