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Inpolitical science,parallel voting orsuperposition refers to the use of two or moreelectoral systems to elect different members of a legislature. More precisely, an electoral system is a superposition if it is a mixture of at least two tiers, which do not interact with each other in any way; one part of a legislature is elected using one method, while another part is elected using a different method, with all voters participating in both. Thus, the final results can be found by calculating the results for each system separately based on the votes alone, then adding them together. A system is called fusion (not to be confused withelectoral fusion) ormajority bonus, another independent mixture of two system but without two tiers. Superposition (parallel voting) is also not the same as "coexistence", in which different districts in the same election use different systems. Superposition, fusion and coexistence are distinct from dependentmixed electoral systems likecompensatory (corrective) and conditional systems.
Most often, parallel voting involves combining awinner-take-all system withparty-list proportional representation (PR).[1] Whilefirst-preference plurality 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% inArmenia.[2] Parallel voting is used in both national parliaments and local governments inTaiwan,Lithuania,Russia,Argentina, and other countries, making it relatively common among the world's electoral systems.
In parallel voting, voters cast two (or more) votes, one for each method the system contains.[citation needed] However, these votes do not interact in any way: the vote in one method has no effect on the calculation of seats in the other methods.
Under the most common form of parallel voting, a portion of seats in thelegislature are filled by thesingle-memberfirst-preference plurality method (FPP), while others are filled byproportional representation.[3] This sometimes leads to ahypercorrection that attempts to limit the term parallel voting to refer only to mixtures of first-past-the-post and proportional representation. Parallel voting can use other systems besides FPP, and can have any mixture ofwinner-take-all,semi-proportional, and proportional components.
Although the two are often mistakenlyconflated,mixed-member majoritarian representation and parallel voting refer to two different things. Parallel voting refers to arule for computing each party's representation in a legislature, which involves two voting systems operating in parallel, with one being layered (superimposed) on top of the other. By contrast, mixed-member majoritarian representation refers to theresults of the system, i.e. the system retains the advantage that some parties get in thewinner-take-all side of the system.
For this reason, parallel voting is not always mixed-member majoritarian. For example, parallel voting may use a two proportional systems like STV and list-PR and then it would not be mixed-member majoritarian, and a majority bonus system (which is not the same as parallel voting) may also be considered mixed majoritarian. In addition, some mixed-member majoritarian systems are not parallel, in that they allow for interaction (limited compensation) between the two components, for example this is the case in South Korea and Mexico. In South Korea, the hybrid of parallel voting and seat linkage compensation, being between the MMP and MMM type of representation has been called mixed-member semi-proportional representation as well.[citation needed]
Unlikemixed-member proportional representation, where party lists are used to achieve an overall proportional result in the legislature, under parallel voting, proportionality is confined only to the list seats. Therefore, a party that secured, say, 5% of the vote will have only 5% of thelist seats, and not 5% of all the seats in the legislature.
The major critique of parallel systems is that they cannot guarantee overall proportionality. Large parties can win very large majorities, disproportionate to their percentage vote.
Parallel voting systems allow smaller parties that cannot win individual elections to secure at least some representation in the legislature; however, unlike in a proportional system they will have a substantially smaller delegation than their share of the total vote. This is seen by advocates of proportional systems to be better than elections using only first-past-the-post, but still unfair towards constituents of smaller parties. If there is also a threshold for list seats, parties which are too small to reach the threshold are unable to achieve any representation, unless they have a very strong base in certain constituencies to gain individual seats.
Smaller parties are still disadvantaged as the larger parties still predominate. Voters of smaller parties may tactically vote for candidates of larger parties to avoid wasting their constituency vote. If the smaller party close to the threshold may refrain from voting for their preferred party in favour of a larger party to avoid wasting their list vote as well. In countries where there is one dominant party and a divided opposition, the proportional seats may be essential for allowing an effective opposition.
Those who favour majoritarian systems argue that supplementary seats allocated proportionally increases the chances that no party will receive a majority in an assembly, leading tominority orcoalition governments.[citation needed]; the largest parties may need to rely on the support of smaller ones in order to form a government. Those who favour proportional representation see this as an advantage as parties may not govern alone, but have to compromise. It is also argued that parallel voting does not lead to the degree of fragmentation found in party systems under pure forms ofproportional representation.[4]
Because voters have two votes, one for a constituency candidate and one for a list, there is a critique that two classes of representatives will emerge under a parallel voting system: with one class beholden to their electorate seat, and the other concerned only with their party. Some consider this as an advantage as local as well as national interests will be represented. Some prefer systems where every constituency and therefore every constituent has only one representative, while others prefer a system where every MP represents the electorate as a whole as this is reflected in the electoral system as well.
Parallel systems are often contrasted withmixed-member proportional systems (MMP) or theadditional member system (AMS). There are a unique set of advantages and disadvantages that apply to these specific comparisons.
A party that cangerrymander local districts can win more than its share of seats. So parallel systems need fair criteria to draw district boundaries. (Under MMP a gerrymander can help a local candidate, but it cannot raise a major party’s share of seats, while under AMS the effects of gerrymandering are reduced by the compensation)
Japan, and subsequentlyThailand andRussia adopted a parallel system to provide incentives for greater party cohesiveness.[5] The party is sure to elect the candidates at the top of its list, guaranteeing safe seats for the leadership. By contrast, under the MMP or AMS system a party that does well in the local seats will not need or receive any compensatory list seats, so the leadership might have to run in the local seats.
Certain types of AMS can be madede facto parallel systems by tactical voting and parties using decoy lists, which (other) MMP systems generally avoid. This specific type of tactical voting does not occur in parallel voting systems as there is no interaction between its systems to exploit in a way that makes it irrelevant. However, other types of tactical voting (such as compromising) are more relevant under parallel voting, than under AMS, and are virtually irrelevant under MMP.[citation needed] Tactical voting by supporters of larger parties in favour of allied smaller parties close to a threshold, to help their entry to parliament are a possibility in any parallel, AMS or MMP system with an electoral threshold.
Parallel systems support the creation of single-party majorities more often than MMP or AMS systems, this may be a positive or a negative depending on the view of the voter.
Parallel voting is currently used in the following countries:[6]
| Country | Body | Members elected in constituencies | Members elected by proportional representation | Other members | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Total | % | System | Total | % | System | Total | System | % | ||
| Realm of New Zealand |  NiueAssembly | 14 | 70% | FPTP | 6 | 30% | Plurality block voting (BV) | |||
| British overseas territories |  AnguillaHouse of Assembly | 7 | 54% | FPTP | 4 | 31% | Plurality block voting (BV) | 2 | 2ex officio | 15% |
 Turks and Caicos IslandsHouse of Assembly | 10 | 48% | FPTP | 5 | 24% | Plurality block voting (BV) | 6 | 4 appointed, 2ex officio | 28% | |
 British Virgin IslandsHouse of Assembly | 9 | 60% | FPTP | 4 | 27% | Plurality block voting (BV) | 2 | 2ex officio | 13% | |
The Philippines' electoral system for Congress is an exceptional case. Political parties running for party-list seats are legally required to be completely separate from those running in constituency seats. Furthermore, political parties are capped at 3 seats (out of 20% of seats, or about 60 seats). As a result, the mixed-member system utilized in the Philippines is not representative at all of the share of the vote that "normal" political parties obtain (even amongst mixed-member majoritarian systems), let alone for those in full proportional representation systems.
InNew Zealand, theRoyal Commission on the Electoral System reviewed the electoral system in 1985–86 and considered parallel voting as a possible replacement for thesingle-member plurality (SMP) system in use at the time.
The commission came to the conclusion that parallel voting would be unable to overcome the shortcomings of New Zealand's previous SMP system. The total seats won by a party would likely remain out of proportion to its share of votes—there would be a "considerable imbalance between share of the votes and share of the total seats"—and it would be unfair to minor parties (who would struggle to win constituency seats).[16] In theindicative 1992 electoral referendum, parallel voting was one of four choices for an alternative electoral system (alongsideMMP,AV andSTV), but came last with only 5.5 percent of the vote. An overwhelming majority of voters supported MMP, as recommended by the Royal Commission, and the system was adopted after the1993 electoral referendum.
Inanother referendum in 2011, 57.77% of voters elected to keep current the MMP system. Among the 42.23% that voted to change to another system, a plurality (46.66%) preferred a return to the pre-1994 SMP system. Parallel voting was the second-most popular choice, with 24.14% of the vote.[citation needed]
