Semi-proportional representation
Semi-proportional representation characterizes multi-winner electoral systems which allow representation of minorities, but are not intended to reflect the strength of the competing political forces in close proportion to the votes they receive.[1] Semi-proportional voting systems are generally used as a compromise between complex and expensive but more-proportional systems (like the single transferable vote) and simple winner-take-all systems.[2][3] Examples of semi-proportional systems include the single non-transferable vote, limited voting, and parallel voting.
Semi-proportional systems[edit]
Most proportional representation systems will not yield precisely proportional outcomes due to the use of election thresholds, small electoral regions, or other implementation details that vary from one elected body to another. However, systems that yield results close to the ideal are generally considered fully-proportional.
The choice to use a semi-proportional electoral system may be a deliberate attempt to find a balance between single-party rule and proportional representation. Semi-proportional systems can allow for fairer representation of those parties that have difficulty gaining even a single seat while retaining the possibility of one party gaining an overall majority of seats even if it receives less than a majority of the votes; they can ensure that the two or three largest parties all have their due share of seats or more while not producing representation for the smallest parties.
Because there are many measures of proportionality,[4][5] and because there is no objective threshold, opinions may differ on what constitutes a semi-proportional system as opposed to a non-proportional one or a fully proportional system.
Partisan systems[edit]
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 majoritarian principle of representation (but not necessarily majoritarianism or majority rule, see electoral inversion and plurality) starting from basic PR mechanisms: parallel voting, the majority bonus system (MBS), and extremely reduced constituency magnitude.
In additional member systems (AMS), the number of additional members may not be sufficient to balance the disproportionality of the original system, thereby producing less than proportional results. When this imbalance is created intentionally, the result could be described as a semi-proportional system — for example, 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. Similarly, in vote transfer based mixed single vote systems, the number of compensatory seats may be too low (or too high) to achieve proportionality.[9] Such a system is used in Hungary in local elections.[10] 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, based on parallel voting, but also including compensatory mechanisms – which however are insufficient for providing proportional results.
A majority bonus system takes an otherwise proportional system based on multi-member constituencies, and introduces disproportionality by granting additional seats to the first party or alliance. Majority bonuses help produce landslide victories similar to those which occur in elections under plurality systems. The majority bonus system was first introduced by Benito Mussolini to win the election of 1924. It has remained in use in Italy, as well as seeing some use in San Marino, Greece, and France.
The simplest mechanism to reinforce major parties in PR system is to severely restrict the number of seats per electoral district, which increases the Droop quota (the number of votes needed to be guaranteed a seat).
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.