Proportional representation is the general name for a class of voting systems that attempt to make the percentage of offices awarded to candidates reflect as closely as possible the percentage of votes that they received in the election. It is the most widely used set of electoral systems in the world, and its variants can be found at some level of government in almost every country (including the United States, where some city councils are elected using forms of PR).
The main features of Proportional Representation (PR) systems are as follows:
List proportional representation (List PR)
- Based on the assumption that parties are the real contestants and the principle that their seat shares should accurately reflect their vote shares
- Requires multi-member districts (the bigger the more proportional the final result can be)
- Counting and seat determination processes are generally complex and not immediately transparent
- Candidates are elected based on the total percentage of votes cast for their party.
- Main models include: List; Mixed Member Proportional; Single Transferable Vote; Single Non-Transferable Vote; Parallel.
Most PR systems use some form of List PR. List PR is used in multi-member electorates where votes are cast in order of preference for the parties which have registered a list of candidates. Parties receive seats in proportion to their overall share of the total vote and winning candidates are taken from the lists in order of their position.
Mixed member proportional (MMP)
MMP systems try to combine the elements of majority and PR systems. A proportion of the parliament is elected by majority methods, usually from single-member electorates, while the remainder come from PR Lists.
Under MMP systems, the List PR seats compensate for any disproportions produced by the district seat results. For example, if one party wins 10% of the national votes but no district seats, they would be awarded enough seats from the PR lists to bring their representation up to around 10% of the parliament.
MMP is used in countries such as Germany, New Zealand, Italy and Venezuela.
The single transferable vote (STV)
The STV system is used in multi-member districts with electors ranking candidates in order of preference on the ballot paper as in PV. Preference marking is usually optional where electors can mark as many candidates as they choose. After the total number of 1st preference votes is added up, the count begins by establishing the quota of votes needed for the election of a single candidate.
One of the most widely used methods is known as the Droop quota, named for the nineteenth-century thinker and mathematician H. R. Droop. The Droop quota is used to determine the minimal number of votes that an individual candidate must get in order to be awarded a seat. It is calculated using the formula:
where V is the total number of valid votes cast in the constituency, and S is the total number seats up for election in the constituency. Hence, if we have 1,000 votes cast for 3 seats, the Droop quota is [ 1,000 / (3 + 1) ] + 1 = 251. That means that any candidate who is able to get at least 251 votes will be assured of winning a seat. Once the Droop quota has been calculated and all the votes collected, we still have to allocate the seats.
All Australian PR systems use the STV, although the South Australian, Victorian, Western Australian and NSW Upper Houses and the federal Senate may be thought of as semi-list systems as the ballot paper also provides for group voting above the line or in the case of Western Australia left and right of the line.
STV is used for national parliamentary elections in Ireland, Malta and Estonia.
Single non-transferable vote (SNTV)
In SNTV systems, each elector has one vote but there are several seats in the district to be filled. The candidates with the highest number of votes fill these positions. For example, In a 4-member district a candidate needs just over 20% of the vote to be elected.
The main difference between SNTV and majority systems is that the SNTV makes it easier for minority parties to be represented. The larger the number of seats in the constituency, the more proportional the system becomes.
The SNTV system is used for parliamentary elections in countries such as Jordan, Taiwan and Vanuatu.
Parallel systems use both PR lists and majority (“winner takes all”) methods but, unlike MMP systems, the PR lists do not compensate for any disproportions within the majority districts.
Parallel systems are used in around 20 countries including Croatia, Japan and Russia.