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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.

Semi-proportional systems

Most proportional representation systems are not precisely proportional due to thresholds, or split electoral regions. But this article deals more with mixed systems that are reasonably close to being proportional but not designed to be as proportional as possible across an entire country.

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 retaining the possibility of one party gaining an overall majority when there is a landslide victory.

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.

Non-partisan systems

Election systems in which 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 systems 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 non-partisan systems is, at least technically, non-partisan. Certainly, a group of candidates can coordinate their campaigns, and politically present themselves as party members, but there is no obligation for electors to respect those party links, and forms of panachage are usually possible.

Single Transferable Vote

Some consider STV to be a semi-proportional system. The degree of proportionality across the country depends on the average size of constituencies. In the 2011 Irish general election, Fine Gael came nine seats (4.8%) short of an overall majority with just 36.1% of the first preference votes. However the result of the election was exceptional, and Fine Gael benefited from a high level of transfers from those who did not rank them first. Under STV a party can win an overall majority with significantly fewer than 50% of the votes, but only if the party also gains a high level of transfers from those who do not rank them first. As it lacks any arbitrary nationwide election threshold, even with the Irish 3 to 5 seat system the level of proportionality does not veer too far from countries with such thresholds.

Partisan systems

Other forms of semi-proportional representation are based on, 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: parallel voting, majority bonuses, and extremely reduced constituency magnitude. An additional member system may reinforce majorities if the proportion of compensatory seats is too low.

A majority bonus system introduces an FPTP-like idea in multi-member constituencies. The bonus gives additional seats to the first party or alliance, to create a landslide victory; this can happen 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, then it was later used in Italy again, with additional democratic limits, and then again expanded in some neighboring countries like San Marino, Greece and France.

The simplest mechanism to reinforce major parties in PR system is a severely reduced constituency magnitude, so to reduce the possibility for minor national parties to gain seats. If the Spanish electoral system is still considered a form of proportional representation, the binomial voting system used in Chile effectively establishes by law a two-party rule over the country.

The last main group usually considered semi-proportional consists of parallel voting models. The system used for the Chamber of Deputies of Mexico since 1996 is considered a parallel voting system, modified by a list-seat ceiling (8%) for over-representation of parties. The "scorporo" system used for the Parliament of Italy from 1993 to 2005 and the electoral system for the National Assembly of Hungary since 1990 are also special cases.

As well, the additional member systems where the additional members are not sufficient to balance the disproportionality of the original system can produce less than proportional results, especially in the National Assembly for Wales where only 33.3% of members are compensatory. The electoral system commonly referred to in Britain as the "additional member system" is also used for the Scottish Parliament, and the London Assembly, with generally proportional results.

References

1. Douglas J. Amy. "Semiproportional voting systems". Retrieved 19 June 2011.
2. Giovanni Sartori, Parties and Party Systems. A framework for analysis. Cambridge, Cambridge University Press.
3. P. Kestelman (June 2005). "Apportionment and Proportionality: A Measured View" (PDF). Retrieved 19 June 2011.
4. 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.
5. "Semi-Proportional Electoral Methods". Retrieved 19 June 2011.

• Semi-proportional electoral systems
• Voting systems