Scorporo

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Scorporo is a mixed member electoral system (sometimes referred to as an additional member system) whereby a portion of members are elected in single member districts (SMDs) and a portion are elected from a list. It may be fully defined as a parallel voting system, but which excludes a portion (up to 100%) of the SMD winners' votes in electing the proportional tier to result in a more proportional outcome. The exclusion of a portion of the SMD winners' votes is what makes scorporo fundamentally different from parallel voting and somewhat closer to mixed member proportional representation, and thereby between the two in terms of proportionality. The system is only known to have been used in Italy and for a portion of the compensatory tier of the National Assembly of Hungary.

Use in Italy

Scorporo was in force for elections to the bicameral Parliament of Italy based on Law 277/1993 from 1993 to 2005. Under this system, members could be elected in two ways:

Approximately 75% of elected members were elected in single member districts (SMDs) using first-past-the-post voting.
Approximately 25% of elected members were elected on list basis based on the proportion of the votes received by the party (using the D'Hondt method), with the exclusion of a proportion of any first placed winner's votes.

The system was subject to the following specific rules for each chamber:

Senate

List seats were calculated at the regional level.
All votes for winning candidates were excluded from the list allocation.
No threshold was applied for list seats.
The SMD vote and the list vote were linked, limiting the use of decoy lists (see below).

Chamber of Deputies

The list seats were calculated at the national level.
The amount of SMD winner's votes excluded from the list vote was equal to the second place candidate's vote total +1. This represented the amount of votes needed to elect the winner in the SMD.
A 4% threshold was established for parties to qualify for the list seats.
The local vote and list vote were not tied to each other, thereby providing an incentive for decoy lists (see below).

Abuse in the 2001 Italian Chamber of Deputies election

In the Italian general election, 2001, one of the two main coalitions (the House of Freedoms, which opposed the system), linked many of their constituency candidates to a decoy list (liste civetta) in the proportional parts, under the name Abolizione Scorporo. As a defensive move, the other coalition, Olive Tree, felt obliged to do the same, under the name Paese Nuovo. This successfully circumvented the compensatory element of proportional lists.

The voters in the constituency seats won by each coalition were still effectively counted in the number of proportional seats they received. Between them, the two decoy lists won 360 of the 475 constituency seats, more than half of the total of 630 seats available, despite winning a combined total of less than 0.2% of the national proportional part of the vote. In the case of Forza Italia (part of the House of Freedoms), the tactic was so successful that it did not have enough candidates in the proportional tier to receive as many seats as it in fact won, missing out on 12 seats.

This was facilitated by the fact that this particular scorporo system allowed the SMD vote and the list voted not to be linked. Decoy lists are a common issue in all compensatory and pseudo-compensatory systems and was not a unique problem for scorporo.

Abolition

Due to Silvio Berlusconi's opposition to the system, Italy reverted to list semi-proportional representation in 2005.

Use in Hungary

The compensatory tier of the National Assembly of Hungary (which follows a type of parallel voting with an additional compensatory systems) is allocated to parties crossing a national 5% threshold based on losing candidates' votes in the first round of single district voting. However, each party's totals are further augmented by "any wasted" votes from the regional list-tier elections (see below).

Proportional systems

Several systems using regional list proportional representation contain a compensatory element similar to scorporo for wasted votes at the district or regional level. Because list PR systems may have more than one candidate elected in a district, typically these systems use "wasted votes" rather than the votes of losing candidates.

Countries that make use of such tiers are:

Hungary (see above)
Austria, which does not use a fixed number of compensatory seats but does allocate votes pertaining to unawarded to fractional seats to its regional and then to a national tier.
Germany proposed a similar compensatory to augment its proposed regionalized MMP as part of its 2009 electoral reform. However, the entire electoral reform law was ruled unconstitutional for other reasons.