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Vote linkage
The vote linkage or (multi-tier) vote transfer system is type of compensatory mixed electoral system, where votes may be transferred across multiple tiers of an electoral system, in order to avoid wasted votes - in contrast to the more common seat linkage compensatory system (commonly referred to as MMP). It often presupposes and is related to the concept of the mixed single vote, which means that the same vote can be used in multiple tiers of an electoral system and that a vote for a local candidate may automatically count as a vote for the candidate's party or the other way around. Voters usually cast their single vote for a local candidate in a single-member district (SMD) and then all the wasted votes from this lower tier are added to distribute seats between upper tier candidates, typically national party lists.
Partially compensatory multi-tier vote linkage is an equivalent of the indirect single transferable vote among multi-tiered electoral systems (except for the mixed ballot transferable vote versions, which are multi-tier equivalents to STV). A related concept is seat linkage, where it is not the votes used in one tier that connect two tiers, but the number of seats a party achieved on the lower tier that is taken into account. A vote linkage system, when applied in a compensatory way takes into account the number of votes that were effective or wasted in the lower tier and takes this into account in the apportionment of the upper tier.
Vote linkage systems currently or formerly used for various national or local elections in Germany, Hungary and Italy have been sometimes described as mixed-majoritarian (similar to common versions of parallel voting), or a unique system between MMM and MMP (seat linkage). Some supermixed systems use vote linkage together with parallel voting (superposition) in a two-vote setup, where split ticket voting is allowed. How proportional the outcome depends on many factors including the vote transfer rules, such which votes are recounted as party list votes, and other parameters (e.g. the number of list seats) used in the system. The vote linkage system originates from Germany and is currently used in Hungary. A version called scorporo was also used in Italy from 1993 to 2005.
Mixed single vote systems may use vote linkage compensation, meaning not all, but only 'wasted' votes get transferred as list votes to the other tier. Some uncommon, supermixed systems use of MSV may add or subtract the discounted list results to establish a vote linkage based element of compensation into system that would otherwise be categorised as parallel voting. Either type of system is misleadingly known in Hungarian as a "fractional vote recounting system" (Hungarian: töredékszavat-visszaszámláló rendszer), however, there are no fractional votes used in any variation, the name merely alluding to only a fraction of votes being "recounted" as list votes.
The third type of mixed single vote system is the single vote equivalent of parallel voting (sometimes called direct vote transfer), which uses the same vote on both the majoritarian and proportional tiers. This makes such systems non-compensatory, falling under the superposition type of mixed systems identified by Massicotte & Blais.
The first recorded mixed vote transfer systems (used in Germany) have been under the "losers plus surplus" model, therefore, they inherently included "winner compensation". Under later definitions of certain sources, this model would also be retroactively a "negative vote transfer system" despite not using any votes with negative transfer value. The confusion stems from the terms "positive" and "negative vote transfer system" being coined based on the systems in use in the 1990s and early 2000s in Hungary and Italy and the inconsistent terminology of sources on these niche variants. While all the Hungarian versions primarily transferred votes with a positive value and the votes transferred were almost exclusively in compensation for losing candidates, the Italian models of scorporo operated only with a negative value and deducted all or a part of votes cast for local winners.
In one view, positive vote transfer means vote transfer with only positive votes value, with or without winner compensation (which may be itself positive or negative). This means that either only the positive transfer votes are used on the list tier to apportion seats (Hungarian local elections), or they are added to other (direct) list votes (Hungarian national elections). Negative vote transfer systems, meanwhile use the opposite principle, they subtract exactly those votes (from the direct list votes), which the equivalent positive vote transfer would not transfer. In this way, these systems rely on negative value winner compensation, which is their most important property that determines how they can be manipulated.
In some sources, the Hungarian model of "losers only" has been labeled "positive vote transfer", under this view the Italian Senate model, despite using only negative transfer votes would also be PVT, since it operates under the same "losers only" principle (deducting all of winners votes from the list vote). Conversely "negative vote transfer" means not only the Italian Chamber model of scorporo is (deducting the non-surplus votes of winners), but the original German variants and the current Hungarian electoral systems for national elections (it uses winner compensation with positive value). A third term of "direct vote transfer" has been used for vote transfer systems without compensation (mixed single vote equivalent of parallel voting). This view has been criticized for using unintuitive terminology and not including models of winner compensation other than the surplus votes compared to the second place candidate[citation needed]. This article uses the former view to maintain consistency and to show the significance of positive/negative transfers on manipulation more intuitively.
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Vote linkage
The vote linkage or (multi-tier) vote transfer system is type of compensatory mixed electoral system, where votes may be transferred across multiple tiers of an electoral system, in order to avoid wasted votes - in contrast to the more common seat linkage compensatory system (commonly referred to as MMP). It often presupposes and is related to the concept of the mixed single vote, which means that the same vote can be used in multiple tiers of an electoral system and that a vote for a local candidate may automatically count as a vote for the candidate's party or the other way around. Voters usually cast their single vote for a local candidate in a single-member district (SMD) and then all the wasted votes from this lower tier are added to distribute seats between upper tier candidates, typically national party lists.
Partially compensatory multi-tier vote linkage is an equivalent of the indirect single transferable vote among multi-tiered electoral systems (except for the mixed ballot transferable vote versions, which are multi-tier equivalents to STV). A related concept is seat linkage, where it is not the votes used in one tier that connect two tiers, but the number of seats a party achieved on the lower tier that is taken into account. A vote linkage system, when applied in a compensatory way takes into account the number of votes that were effective or wasted in the lower tier and takes this into account in the apportionment of the upper tier.
Vote linkage systems currently or formerly used for various national or local elections in Germany, Hungary and Italy have been sometimes described as mixed-majoritarian (similar to common versions of parallel voting), or a unique system between MMM and MMP (seat linkage). Some supermixed systems use vote linkage together with parallel voting (superposition) in a two-vote setup, where split ticket voting is allowed. How proportional the outcome depends on many factors including the vote transfer rules, such which votes are recounted as party list votes, and other parameters (e.g. the number of list seats) used in the system. The vote linkage system originates from Germany and is currently used in Hungary. A version called scorporo was also used in Italy from 1993 to 2005.
Mixed single vote systems may use vote linkage compensation, meaning not all, but only 'wasted' votes get transferred as list votes to the other tier. Some uncommon, supermixed systems use of MSV may add or subtract the discounted list results to establish a vote linkage based element of compensation into system that would otherwise be categorised as parallel voting. Either type of system is misleadingly known in Hungarian as a "fractional vote recounting system" (Hungarian: töredékszavat-visszaszámláló rendszer), however, there are no fractional votes used in any variation, the name merely alluding to only a fraction of votes being "recounted" as list votes.
The third type of mixed single vote system is the single vote equivalent of parallel voting (sometimes called direct vote transfer), which uses the same vote on both the majoritarian and proportional tiers. This makes such systems non-compensatory, falling under the superposition type of mixed systems identified by Massicotte & Blais.
The first recorded mixed vote transfer systems (used in Germany) have been under the "losers plus surplus" model, therefore, they inherently included "winner compensation". Under later definitions of certain sources, this model would also be retroactively a "negative vote transfer system" despite not using any votes with negative transfer value. The confusion stems from the terms "positive" and "negative vote transfer system" being coined based on the systems in use in the 1990s and early 2000s in Hungary and Italy and the inconsistent terminology of sources on these niche variants. While all the Hungarian versions primarily transferred votes with a positive value and the votes transferred were almost exclusively in compensation for losing candidates, the Italian models of scorporo operated only with a negative value and deducted all or a part of votes cast for local winners.
In one view, positive vote transfer means vote transfer with only positive votes value, with or without winner compensation (which may be itself positive or negative). This means that either only the positive transfer votes are used on the list tier to apportion seats (Hungarian local elections), or they are added to other (direct) list votes (Hungarian national elections). Negative vote transfer systems, meanwhile use the opposite principle, they subtract exactly those votes (from the direct list votes), which the equivalent positive vote transfer would not transfer. In this way, these systems rely on negative value winner compensation, which is their most important property that determines how they can be manipulated.
In some sources, the Hungarian model of "losers only" has been labeled "positive vote transfer", under this view the Italian Senate model, despite using only negative transfer votes would also be PVT, since it operates under the same "losers only" principle (deducting all of winners votes from the list vote). Conversely "negative vote transfer" means not only the Italian Chamber model of scorporo is (deducting the non-surplus votes of winners), but the original German variants and the current Hungarian electoral systems for national elections (it uses winner compensation with positive value). A third term of "direct vote transfer" has been used for vote transfer systems without compensation (mixed single vote equivalent of parallel voting). This view has been criticized for using unintuitive terminology and not including models of winner compensation other than the surplus votes compared to the second place candidate[citation needed]. This article uses the former view to maintain consistency and to show the significance of positive/negative transfers on manipulation more intuitively.