Mixed electoral system

A mixed electoral system is an electoral system that combines a plurality/majoritarian voting system with an element of proportional representation (PR). The plurality/majoritarian component is usually first-past-the-post voting (FPTP), whereas the proportional component is most often based on party list PR. A distinguishing characteristic of mixed systems is the fact that every voter can influence both the plurality/majoritarian and PR aspects of an election. In a hybrid system, by contrast, different electoral formulas are used in different regions of a country.

The most prominent mixed electoral systems include mixed member proportional (MMP) and parallel voting, that latter of which is also known as mixed member majoritarian (MMM). MMP generally produces proportional election outcomes, meaning that a political party which wins n% of the vote will receive roughy n% of the seats. Parallel voting tends to produce semi-proportional outcomes: more proportional than a plurality/majoritarian system but less proportional than a PR electoral system. Both parallel voting and MMP feature two tiers of elected representatives: one associated with the plurality/majoritarian component and one associated with PR. It is not necessary, however, for a mixed system to have multiple electoral tiers.

A distinction is often made between mixed compensatory systems and mixed non-compensatory systems. In both types of systems, one set of seats is allocated using a plurality/majoritarian method. The remaining seats are allocated to political parties using a proportional allocation method such as highest averages or largest remainder. In mixed non-compensatory systems, which are also known as a parallel systems, the proportional allocation is performed independently of the plurality/majoritarian component. In mixed compensatory systems, the allocation of PR seats is adjusted to compensate for disproportionality caused by the plurality/majoritarian component.

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