|Part of the Politics series|
A semi-proportional voting system is a multi-winner voting system which allows representation of minorities, but does not reflect the strength of the competing political forces proportionally, mixing the principles of proportional representation and plurality voting.
The choice to use a semi-proportional voting system may be a deliberate attempt to find a balance between majority rule and proportional representation: semi-proportional systems can allow for fairer representation of those parties that have difficulty gaining individual seats while still keeping the possibility of one party gaining a majority when there is a landslide victory. On the other hand, the semi-proportional nature of a legislature may arise unintended, from the dynamics of the system itself.
Because there are many measures of proportionality, and because there is no objective threshold, opinions on what constitutes a semi-proportional method rather than a majoritarian or a fully proportional one, may differ.
Methods where parties can only achieve proportionality by coordinating their voters are usually considered to be semi-proportional. They are not majoritarian, since in the perfect case, the outcome will be proportional, but they are not proportional either, since such a perfect case requires a very high degree of coordination. Such methods include the single non-transferable vote and limited voting, the latter of which becomes less proportional the more votes each voter has. The cumulative voting also allows minority representation, concentrating votes over the number of candidates that every minor party thinks it can support.
This group of system are, at least technically, non-partisan. Surely, group of candidates can cohordinate their campaigns, and politically present themselves as party members, but there is no obligation for electors to respect these party links, and forms of panachage are usually possible.
Other forms of semi-proportional representation are based, or at least use, party lists to work. Looking to the electoral systems effectively in use around the world, there are three general methods to reinforce the majority rule starting from basic PR mechanisms: majority bonuses, extremely reduced constituency magniture, or additional member systems.
A majority bonus introduce a FPTP-like idea in multi-member constituencies. The bonus gives additional seats to the first party or alliance, to create a landslide victory as it happens in countries using the FPTP even if single-member constituencies are not in use. The majority bonus system was firstly introduced by Benito Mussolini to win the election of 1924, but it was later used in Italy again, with additional democratic limits, and then expanded in some neighbor countries like San Marino, Greece and France.
The most simple mechanism to reinforce major parties in PR system is a reduced constituency magniture, so to reduce the possibility for minor national parties to gain seats. If the Spanish electoral system is still considered a form of proportinal representation, the binomial system used in Chile effectively establish by law a two-party rule over the country.
The last main group usually considered semi-proportional consists of additional member systems where the additional members are not apportioned to counter imbalance in party proportionality, or where the manner in which they are so done is not sufficient to balance the disproportionality of the original system. The first subgroup includes parallel voting, and the second, the electoral system commonly referred to in Britain as the "additional member system", used for the Scottish Parliament, National Assembly for Wales, and London Assembly, the "scorporo" system used for the Parliament of Italy from 1993 to 2005, the electoral system for the National Assembly of Hungary since 1990, and the system used for the Chamber of Deputies of Mexico since 1996, though this last is perhaps better considered a parallel voting system, modified by a list-seat ceiling (8%) for over-representation of parties.
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- Giovanni Sartori, Parties and Party Systems. A framework for analysis. Cambridge, Cambridge University Press.
- P. Kestelman (June 2005). "Apportionment and Proportionality: A Measured View". Retrieved 19 June 2011.
- Barry R. Weingast; Donald A. Wittman (19 October 2006). The Oxford handbook of political economy. Oxford University Press. pp. 105–. ISBN 978-0-19-927222-8. Retrieved 19 June 2011.
- "Semi-Proportional Electoral Methods". Retrieved 19 June 2011.