Vote linkage
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.
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[7][8] (similar to common versions of parallel voting), or a unique system between MMM and MMP (seat linkage).
[4] In this way, these systems rely on negative value winner compensation, which is their most important property that determines how they can be manipulated.
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).
[11] 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].
[13] Together with other criticisms of the change (suspicions of gerrymandering, moving towards an even more mixed-majoritarian system, postal voting for non-resident citizens only etc.)
this was viewed as a thinly veiled attempt to benefit the parties who created the system, without meaningful consultation of the opposition.
(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) Seat linkage and vote linkage systems both suffer from different potential manipulation strategies arising from their compensatory component, which the following table shows.
German opposition to a purely winner-take-all system like first-past-the-post, that the British preferred, necessitated a compromise.
The vote transfer system which was of the "losers plus surplus model"[6] included winner compensation and the majority of seats were won in single-member district would mostly keep the result as close to first-past-the-post as possible (see mixed-member majoritarian representation), while allowing for some compensatory representation of other parties ('The British called this a "modified PR system".
The system, however, had some small negative value winner compensation from the party-list PR of the regional multi-member districts as well.
[9] National Assembly elections use a positive vote transfer system,[16] which also partially 'compensates' parties of winning candidates.
However, because there are effectively no votes transferred with a negative value, the system is not subject to the same decoy list tactics as scorporo is.
A negative vote transfer system called scorporo was in force for elections to the bicameral Parliament of Italy based on Law 277/1993 from 1993 to 2005.
This list was not designed to win proportional seats, but only to soak up constituency votes for House of Freedoms, enabling them to win a larger share of the proportional list seats than they would be entitled to if all candidates were linked other House of Freedoms parties.
As a defensive move, the other coalition, The Olive Tree, created their own decoy list under the name Paese Nuovo (New Country).
Decoy lists are a common issue in all compensatory and pseudo-compensatory systems, and this was not a unique problem for scorporo.
[2] The mixed ballot transferable vote (MBTV) was proposed as a preferential variant of the mixed single vote where voters may indicate their preferences separately, and the original proposal also explores methods to make the system relatively proportional (as modifications to the systems used in Hungary).
[12] A system using a mixed single vote in dual member districts (with local lists up to two candidates) called dual-member proportional has been proposed for Canada by Sean Graham.
