Mixed electoral system


A mixed electoral system is an electoral system that combines a plurality/majoritarian voting system with an element of proportional representation. The plurality/majoritarian component is usually first-past-the-post voting, 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 representation and parallel voting, of which the latter is also known as mixed member majoritarian. 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.

Compensatory/non-compensatory seat allocation

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.
The following hypothetical example by Massicotte illustrates how PR seats are typically allocated with compensation and without. The example assumes a 200-seat legislative assembly where 100 seats are filled using FPTP and the other 100 seats are awarded to parties using a form of PR. The table below gives the popular vote and FPTP results. The number of PR seats allocated to each party depends on whether compensation is used.
PartyPopular voteFPTP seatsPR seatsTotal seats
Party A44%65??
Party B40%34??
Party C10%1??
Party D6%0??
TOTAL100%100100200

Without compensation, each party wins its proportional share of the 100 PR seats. However, as shown below, the total number of seats is not proportional to the popular vote. Party A only slightly outperformed Party B according to the popular vote, but receives significantly more seats due to its success in the FPTP contests.
PartyPopular voteFPTP seatsPR seats Total seats
Party A44%6544109
Party B40%344074
Party C10%11011
Party D6%066
TOTAL100%100100200

However, if the PR seats are allocated in a fully compensatory manner, then the total number of seats awarded to each party is proportional to the popular vote. As shown below, Party B wins 34% of the FPTP seats, is awarded 46% of the PR seats, and ends up with 40% of the seats in the assembly.
PartyPopular voteFPTP seatsPR seats Total seats
Party A44%652388
Party B40%344680
Party C10%11920
Party D6%01212
TOTAL100%100100200

In practice, compensatory seat allocation is complicated by the possibility that one or more parties wins so many seats under the plurality/majoritarian component that the designated number of PR seats is insufficient to produce a fully proportional outcome. Some mixed compensatory systems have rules that address these situations by adding extra PR seats until the next election.

Types of mixed systems

Parallel voting

Parallel voting is a mixed non-compensatory system with two tiers of representatives: a tier of single-member district representatives elected by a plurality/majoritarian method such as FPTP, and a tier of regional or at-large representatives elected by a separate proportional method such as party list PR. It is used for the first chamber in many countries including Japan, South Korea, Taiwan, and Russia.
"單一選區兩票制（Single-District Two-Votes System）" for Chinese.

Mixed member proportional

Similar to parallel voting, MMP has a tier of district representatives typically elected by FPTP, and a tier of regional or at-large representatives elected by PR. Unlike parallel voting, MMP is a mixed compensatory system, meaning that the PR seats are allocated in a manner that corrects disproportionality caused by the district tier. MMP is used by Germany, Bolivia, Lesotho, and New Zealand. The additional member system refers to MMP models used in parts of the UK, where small regions with a fixed number of seats tend to produce only moderately proportional election outcomes.

Alternative vote plus

AV+ is a mixed compensatory system similar to the additional member system, with the notable difference that the district seats are awarded using the alternative vote. The system was proposed by the Jenkins Commission as a possible alternative to FPTP for elections to the Parliament of the United Kingdom.

Scorporo

Scorporo is a two-tier mixed system similar to MMP, except that disproportionality caused by the single-member district tier is partially addressed through a vote transfer mechanism. Votes that are crucial to the election of district-winning candidates are excluded from the PR seat allocation. The system was used in Italy from 1993 to 2005, and is currently used in Hungary.

Majority bonus

Electoral systems with a majority bonus have been referred to as "unconventional mixed systems". Employed by Armenia, Greece, and San Marino, as well as Italy from 2006 to 2013, majority bonuses help the most popular party or alliance win a majority of the seats with a minority of the votes, similar in principle to plurality/majoritarian systems. However, PR is used to distribute seats among the opposition parties, and possibly within the governing alliance.

Dual member proportional

DMP is a mixed compensatory system similar to MMP, except that the plurality and PR seats are paired and dedicated to dual-member districts. Proposed as an alternative to FPTP for Canadian elections, DMP appeared as an option on a 2016 plebiscite in Prince Edward Island and a 2018 referendum in British Columbia.

List of countries using mixed systems

The table below lists the countries that use a mixed electoral system for the first chamber of the legislature. Countries with hybrid systems have been excluded from the table, as have countries that mix two plurality/majoritarian systems.
CountryType of mixed system
AndorraParallel voting
ArmeniaMajority bonus
BoliviaMixed member proportional
GeorgiaParallel voting
GermanyMixed member proportional
GreeceMajority bonus
GuineaParallel voting
Hong KongParallel voting
HungaryScorporo
ItalyParallel voting
JapanParallel voting
JordanParallel voting
LesothoMixed member proportional
LithuaniaParallel voting
MauritaniaParallel voting
MexicoParallel voting
MonacoParallel voting
MongoliaParallel voting
MoroccoParallel voting
NepalParallel voting
New ZealandMixed member proportional
PhilippinesParallel voting
RussiaParallel voting
San MarinoMajority bonus
ScotlandAdditional member system
SenegalParallel voting
SeychellesParallel voting
South KoreaParallel voting
Sri LankaParallel voting
TaiwanParallel voting
TajikistanParallel voting
TanzaniaParallel voting
ThailandParallel voting
UkraineParallel voting
VenezuelaParallel voting
ZimbabweParallel voting