Compensation (electoral systems)

Compensation or correction is an optional mechanism of electoral systems, which corrects the results of one part of the system based on some criterion to achieve a certain result, usually to make it more proportional. There are in general two forms of compensation: vote linkage and seat linkage.

Compensation exists in many ranked voting systems such as instant-runoff voting and single transferable voting, where votes for eliminated candidates (and in the case of STV, surplus votes of elected candidates) are transferred to other candidates, thereby compensating voters who voted for candidates who may not be elected (or whose votes were not needed to get a candidate elected). This is an example of vote linkage compensation in a single-tier system. The equivalent of this type of compensation in case of party-list proportional representation is the spare vote.

In mixed electoral systems compensation is usually contrasted with superposition, which means two electoral systems are used independently of each other with multiple tiers. Most mixed compensatory electoral systems use seat linkage (typically mixed-member proportional representation), however some use multi-tier vote linkage, which usually leads to less proportional results.

The two common ways compensation occurs are seat linkage compensation (or top-up) and vote linkage compensation (or vote transfer). Like a non-compensatory mixed system, a compensatory mixed system may be based on the mixed single vote (voters vote for a local candidate and that vote is used to set the party share of the popular vote for the party that the candidate belongs to) or it may be based on voters casting two separate votes.

In both mixed compensatory systems and mixed non-compensatory systems, two sets of seats are allocated using different methods. Most often, this involves one winner-take-all system, usually first-preference plurality. The remaining seats are allocated to political parties partially or wholly based on a proportional allocation method such as highest averages or largest remainder. The difference is whether or not the results of the district elections are considered when allocating the PR seats.^{[citation needed]}

In mixed non-compensatory systems, such as parallel voting, the proportional allocation is performed independently of the district election component.

In seat linkage mixed compensatory systems, the allocation of the top-up seats is done in such a way as to compensate as much as possible for dis-proportionality produced by the district elections. MMP generally produces proportional election outcomes, meaning that a political party that wins n percent of the vote will receive roughly n percent of the seats.^{[citation needed]}

The following hypothetical example based on the one by Massicotte illustrates how "top-up" PR seats are typically allocated in a compensatory system and in a non-compensatory system. 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 the system is compensatory or non-compensatory.^{[citation needed]}