Proportional representation
Proportional representation (PR) refers to any type of electoral system under which subgroups of an electorate are reflected proportionately in the elected body.[1] The concept applies mainly to political divisions (political parties) among voters. The essence of such systems is that all votes cast – or almost all votes cast – contribute to the result and are effectively used to help elect someone – not just a bare plurality or (exclusively) the majority – and that the system produces mixed, balanced representation reflecting how votes are cast.
"Proportional rule" redirects here. For the division rule in financial law, see Proportional rule (bankruptcy).
In the context of voting systems, PR means that each representative in an assembly is elected by a roughly equal number of voters. In the common case of electoral systems that only allow a choice of parties, the seats are allocated in proportion to the vote share each party receives.
The term "proportional representation" may also be used to mean fair representation by population as applied to states, regions, etc. However, representation being proportional with respect solely to population size is not considered to make an electoral system "proportional" the way the term is usually used. For example, the US House of Representatives has 435 members, who each represent a roughly equal number of people and each state is allocated a number of members in accordance with its population size, thus producing representation by population. But members of the House are elected in single-member districts generally through first-past-the-post elections: single-winner contests are not proportional by vote share as each has only one winner. Conversely, PR electoral systems are typically proportional to both population (seats per set amount of population) and vote share (typically party-wise). The European Parliament gives each member state a number of seats roughly based on its population size (see degressive proportionality) and in each member state, the election must also be held using a PR system (with proportional results based on vote share).
The most widely used families of PR electoral systems are party-list PR, used in 85 countries,[2] mixed-member PR (MMP), used in 7 countries,[3] and the single transferable vote (STV), used in Ireland,[4] Malta, the Australian Senate, and Indian Rajya Sabha.[5][6] All PR systems require multi-member voting districts, meaning votes are pooled to elect multiple representatives at once. Pooling may be done in various multi-member districts (in STV and most list PR systems) or in single countrywide – so called at-large – district (in other list-PR systems). A country-wide pooling of votes to elect more than a hundred members is used in Angola, for example. For large districts, party-list PR is more often used. A purely candidate-based PR system, STV, has never been used to elect more than 21 in a single contest to this point in history. Some PR systems use at-large pooling or regional pooling in conjunction with single-member districts (such as the New Zealand MMP and the Scottish additional member system), others use at-large pooling in conjunction with multi-member districts (Scandinavian countries). In these cases, pooling is used to allocate leveling seats (top-up) to compensate for the disproportional results produced in single-member districts using FPTP (MMP/AMS) or to increase the fairness produced in multi-member districts using list PR (Denmark's MMP). PR systems that achieve the highest levels of proportionality tend to use as general pooling as possible (typically country-wide) or districts with large numbers of seats.
Due to various factors, perfect proportionality is rarely achieved under PR systems. The use of electoral thresholds (in list-PR or MMP), small districts with few seats in each (in STV or list-PR), absence or insufficient number of leveling seats (in list-PR, MMP or AMS) may produce disproportionality. Other sources are electoral tactics that may be used in certain system, such as party splitting in some MMP systems. Nonetheless, PR systems approximate proportionality much better than other systems[7] and are more resistant to gerrymandering and other forms of manipulation.
Attributes of PR systems[edit]
District magnitude[edit]
Academics agree that the most important influence on proportionality is an electoral district's magnitude, the number of representatives elected from the district. As magnitude increases, proportionality improves.[19] Some scholars recommend for STV voting districts of roughly four to eight seats,[41] which are considered small relative to PR systems in general, which frequently have district magnitudes in the hundreds.
At one extreme, the binomial electoral system used in Chile between 1989 and 2013,[42] a nominally proportional open-list system, features two-member districts. As this system can be expected to result in the election of one candidate from each of the two dominant political blocks in most districts, it is not generally considered proportional.[19]: 79
At the other extreme, where the district encompasses the entire country (and with a low minimum threshold, highly proportionate representation of political parties can result), parties gain by broadening their appeal by nominating more minority and women candidates.[19]: 83
After the introduction of STV in Ireland in 1921, district magnitudes slowly diminished as more and more three-member constituencies were defined, benefiting the dominant Fianna Fáil, until 1979 when an independent boundary commission was established reversing the trend.[43] In 2010, a parliamentary constitutional committee recommended a minimum magnitude of four.[44] Despite relatively low magnitudes, Ireland has generally experienced highly proportional results.[19]: 73
In the FairVote plan for STV (which FairVote calls choice voting) for the US House of Representatives, three- to five-member super-districts are proposed.[45]
In Professor Mollison's plan for STV in the UK, four- and five-member districts are mostly used, with three and six seat districts used as necessary to fit existing boundaries, and even two and single member districts used where geography dictates.[29]
Electoral threshold[edit]
The electoral threshold is the minimum vote required to win one seat. The lower the threshold, the higher the proportion of votes contributing to the election of representatives and the lower the proportion of votes wasted.[19]
All electoral systems have electoral thresholds, either formally defined or the natural threshold, which is the mathematical consequence of the district magnitude and election parameters.[19]: 83
A formal threshold usually requires parties to win a certain percentage of the vote in order to be awarded seats from the party lists. In Germany and New Zealand (both MMP), the threshold is 5% of the national vote but the threshold is not applied to parties that win a minimum number of constituency seats (three in Germany, one in New Zealand). Turkey defines a threshold of 7%,[46] the Netherlands 0.67%.[19] Israel has raised its threshold from 1% (before 1992) to 1.5% (up to 2004), 2% (in 2006) and 3.25% in 2014.[47] South Africa has no explicit electoral threshold, only a natural threshold ~0.2%. A list of electoral thresholds by country shows a typical electoral threshold for party-list PR is 3-5%.
In STV elections, winning the quota (ballots/(seats+1)plus 1) of votes assures election.[48] Winning the quota in the first count when first preference votes are all that are counted, assures election at that point.[49] E.g. for a district magnitude of 3, the STV electoral threshold would be 25% (of first-preference votes plus transferred later-preference votes), significantly higher than typical party-list PR. However, candidates who receive only about half the quota of first preference votes alone may attract good second (and third, etc.) preference support and win election.[29]
However success with less than quota cannot be relied on. Sometimes candidates in winning positions in the first count (but who do not have quota) are not elected, being pushed aside during the vote count in favor of other candidates who were initially less popular but have wide support and benefit from vote transfers. The need to attract second preferences tends to promote consensus and to disadvantage extremes. Those who do not have wide support may not benefit greatly from vote transfers so may not be elected if they do not receive quota on first count.[49]
The electoral threshold has different effects on STV than on Party-list PR. For STV the votes for candidates below natural threshold are not wasted, but transferred to the next-indicated choice. For party-list PR a vote for a party below electoral threshold is a wasted vote unless the spare vote system is applied.
Party magnitude[edit]
Party magnitude is the number of candidates elected from one party in one district. As party magnitude increases a more balanced ticket will be more successful, encouraging parties to nominate women and minority candidates for election.[50]
But under STV, nominating too many candidates can be counter-productive, splitting the first-preference votes and allowing the candidates to be eliminated before receiving transferred votes from other parties. An example of this was identified in a ward in the 2007 Scottish local elections where Labour, putting up three candidates, won only one seat while they might have won two had one of their voters' preferred candidates not stood.[29] The same effect may have contributed to the collapse of Fianna Fáil in the 2011 Irish general election.[51] But generally in STV contests the transfers of votes allows each party to take roughly its due share of the seats based on vote tallies of the party's candidates and where all the candidates of a party preferred by a voter are eliminated, the vote may be transferred to a candidate of a different party also preferred by the voter.[52]
Others[edit]
Other aspects of PR can influence proportionality such as the size of the elected body, the choice of open or closed lists, ballot design, and vote counting methods.
Exact proportionality has a single unambiguous definition: the seat shares must exactly equal the vote shares, measured as seats-to-votes ratio. When this condition is violated, the allocation is disproportional, and it may be interesting to examine the degree of disproportionality – the degree to which the number of seats won by each party differs from that of a perfectly proportional outcome. This degree does not have a single unambiguous definition. Some common disproportionality indexes are:[53]
The disproportionality changes from one election to another depending on voter behavior and size of effective electoral threshold, here shown is the wasted vote for New Zealand.[54] In 2005 New Zealand general election every party above 1% got seats due to the electoral threshold in New Zealand of at least one seat in first-past-the-post voting, which caused a much lower wasted vote compared to the other years.
Different indexes measure different concepts of disproportionality. Some disproportionality concepts have been mapped to social welfare functions.[55]
Disproportionality indexes are sometimes used to evaluate existing and proposed electoral systems. For example, the Canadian Parliament's 2016 Special Committee on Electoral Reform recommended that a system be designed to achieve "a Gallagher score of 5 or less". This indicated a much lower degree of disproportionality than observed in the 2015 Canadian election under first-past-the-post voting, where the Gallagher index was 12.[56]
There are various other measures of proportionality, some of them have software implementation.[57]
The common indexes (Loosemore–Hanby, Gallagher, Sainte-Laguë) do not support ranked voting.[58][59] An alternative that does support it is the Droop proportionality criterion (DPC). It requires that if, for some set M of candidates, there exist more than k Droop quotas of voters who rank them at the top |M| positions, then at least k candidates from M are elected. In the special case in which voters vote solely by party, DPC implies proportionality.
History[edit]
Pre–19th century[edit]
One of the earliest proposals of proportionality in an assembly was by John Adams in his influential pamphlet Thoughts on Government, written in 1776 during the American Revolution:
Incentives for choosing an electoral system[edit]
Changing the electoral system requires the agreement of a majority of the currently selected legislators, who were chosen using the incumbent electoral system. Therefore, an interesting question is what incentives make current legislators support a new electoral system, particularly a PR system.
Many political scientists argue that PR was adopted by parties on the right as a strategy to survive amid suffrage expansion, democratization and the rise of workers' parties. According to Stein Rokkan in a seminal 1970 study, parties on the right opted to adopt PR as a way to survive as competitive parties in situations when the parties on the right were not united enough to exist under majoritarian systems.[153] This argument was formalized and supported by Carles Boix in a 1999 study.[154] Amel Ahmed notes that prior to the adoption of PR, many electoral systems were based on majority or plurality rule, and that these systems risked eradicating parties on the right in areas where the working class was large in numbers. He therefore argues that parties on the right adopted PR as a way to ensure that they would survive as potent political forces amid suffrage expansion.[155] A 2021 study linked the adoption of PR to incumbent fears of revolutionary threats.[156]
In contrast, other scholars argue that the choice to adopt PR was also due to a demand by parties on the left to ensure a foothold in politics, as well as to encourage a consensual system that would help the left realize its preferred economic policies.[157] The pressure to change may become so great that the government feels it must give in to the demand, even if it itself does not benefit from the change. This is the same process by which women's suffrage was achieved in many countries.[158]