How party-list PR works

Party list PR is the most commonly used version of proportional representation. Voters cast votes for parties and each party is allocated seats based on its party share.

Some party-list PR systems use overall country-wide vote counts; others count vote shares in separate parts of the country and allocate seats in each part according to that specific vote count. Some use both.

List PR involves parties in the election process. Voters do not primarily vote for candidates (persons), but for electoral lists (or party lists), which are lists of candidates that parties put forward. The mechanism that allocates seats to the parties/lists is how these systems achieve proportionality. Once this is done, the candidates who take the seats are based on the order in which they appear on the list. This is the basic, closed list version of list PR.

An example election where the assembly has 200 seats to be filled is presented below. Every voter votes for the list created by their favourite party and the results of the election are as follows (popular vote). Under party-list PR, every party gets a number of seats proportional to their share of the popular vote.

Party		Popular vote	Party-list PR – Sainte-Laguë method
			Number of seats	Seats %
	Party A	43.91%	88	44%
	Party B	39.94%	80	40%
	Party C	9.98%	20	10%
	Party D	6.03%	12	6%
TOTAL		100%	200	100%

This is done by a proportional formula or method; for example, the Sainte-Laguë method – these are the same methods that may be used to allocate seats for geographic proportional representation (for example, how many seats each states gets in the US House of Representatives). Votes and seats often cannot be mathematically perfectly allocated, so some amount of rounding has to be done. The various methods deal with this in different ways, although the difference is reduced if there are many seats – for example, if the whole country is one district. Party list PR is also more complicated in reality than in the example, as countries often use more than one district, multiple tiers (e.g. local, regional and national), open lists or an electoral threshold. This can mean that final seat allocations are frequently not proportional to the parties' vote share.

How the single transferable vote (STV) works

The single transferable vote is an older method than party-list PR, and it does not need to formally involve parties in the election process. Instead of parties putting forward ordered lists of candidates from which winners are drawn in some order, candidates run by name, each voter marks preferences for candidates, with only one marked preference used to place the vote, and votes cast for the candidates determine the winner. This is done using a preferential ballot. The ranking is used to instruct election officials of how the vote should be used in case it is placed on an un-electable candidate or on an elected candidate. Each voter casts one vote and the district used elects multiple members (more than one, usually 3 to 7). Because parties play no role in the vote count, STV may be used for nonpartisan elections, such as the city council of Cambridge, Massachusetts.^[9] A large proportion of the votes cast are used to actually elect someone so the result is mixed and balanced with no one voting block taking much more than its due share of the seats. Where party labels are indicated, proportionality party-wise is noticeable.

Counting votes under STV is more complicated than first-past-the-post voting, but the following example shows how the vote count is performed and how proportionality is achieved in a district with 3 seats. In reality, districts usually elect more members than that in order to achieve more proportional results. A risk is that if the number of seats is larger than, for example, 10 seats, the ballot will be so large as to be inconvenient and voters may find it difficult to rank the many candidates, although 21 are elected through STV in some elections with no great difficulty.^[10] (In many STV systems, voters are not required to mark more choices than desired. Even if all voters marked only one preference, the resulting representation would be more balanced than under single-winner FPTP.)

Under STV, an amount that guarantees election is set, which is called the quota. In this example, the Droop quota is used and so a candidate who earns more than 25 percent of the vote is declared elected. Note that it is only possible for 3 candidates to each achieve that quota.

In the first count, the first preferences (favourite candidates) of all the voters are counted. Any candidates who pass the quota are declared elected.

Simplified example of an STV ballot

Next, the votes the candidates received above the quota (surplus votes that they did not need to get elected) are transferred to the next preferences of the voters who voted for them. We start with Jane Doe's surplus. For the example, we suppose that all voters of Jane Doe prefer John Citizen as their second choice (as he is also from Party A). Based on this, we transfer the surplus votes and find that John Citizen has passed the quota and so is declared elected to the third and last seat that we had to fill. Even if we assume that Fred Rubble's surplus would have gone to Mary Hill, the vote transfer plus Hill's original votes would not add up to quota. Party B did not have two quotas of votes so was not due two seats, while Party A was. It is possible in realistic STV elections for a candidate to win without quota if they are still in the running when the field of candidates has thinned to the number of remaining open seats.

The district result is balanced party-wise. No one party took all the seats, as frequently happens under FPTP or other non-proportional voting systems. The result is fair – the most popular party took two seats; the less popular party took just one. The most popular candidates in each party won the party's seats. 81 percent of the voters saw their first choice elected. At least 15 percent of them (the Doe 1, Citizen 2 voters) saw both their first and second choices elected – there were likely more than 15 percent if some "Citizen 1" votes gave their second preference to Doe. Every voter had satisfaction of seeing someone of the party they support elected in the district.

How mixed-member proportional representation (MMP) works

Mixed Member Proportional Representation combines election of district members with election of additional members as compensatory top-up.

Often MMP systems use single-member districts to elect district members. (Denmark, Iceland and Sweden uses multi-member districts in their MMP systems). MMP with SMDs is described here.

The mixed-member proportional system combines single member plurality voting (SMP), also known as first-past-the-post (FPTP), with party-list PR in a way that the overall result of the election is supposed to be proportional. The voter may vote for a district candidate as well as a party. The main idea behind MMP is compensation, meaning that the list-PR seat allocation is not independent of the results of the district level voting. First-past-the-post is a single winner system and cannot be proportional (winner-takes-all), so these disproportionalities are compensated by the party-list component.

A simple, yet common version of MMP has as many list-PR seats as there are single-member districts. In the example it can be seen, as is often the case in reality, that the results of the district elections are highly disproportional: large parties typically win more seats than they should proportionally, but there is also randomness – a party that receives more votes than another party might not win more seats than the other. Any such dis-proportionality produced by the district elections is addressed, where possible, by the allocation of the compensatory additional members.

Party			Popular vote	FPTP seats (Number of districts won)	Compensatory seats under MMP (party-list PR seats)	Total number of seats under MMP		Seats % under MMP
		Party A	43.91%	64	24	88		44%
		Party B	39.94%	33	47	80		40%
		Party C	9.98%	0	20	20		10%
		Party D	6.03%	3	9	12		6%
TOTAL			100%	100	100	200		100%

MMP gives only as many compensatory seats to a party as they need to have the number of seats of each party be proportional. Another way to say this is that MMP focuses on making the final outcome proportional.

Differences to parallel voting

Compare the MMP example to parallel voting. Parallel voting is a mixed-member majoritarian system. Here the party-list PR seat allocation is independent of the district results, meaning that there is no compensation (no regard to how the district seats were filled). The popular vote, the number of districts won by each party, and the number of districts and party-list PR seats are all the same as in the MMP example above, yet the total number of seats is different.

Party			Popular vote	FPTP seats (Number of districts won)	Party-list PR seats under parallel voting	Total number of seats under parallel voting		Seats % under parallel voting
		Party A	43.91%	64	44	108		54.0%
		Party B	39.94%	33	40	73		36.5%
		Party C	9.98%	0	10	10		5.0%
		Party D	6.03%	3	6	9		4.5%
TOTAL			100%	100	100	200		100%

The overall results are not proportional, although they are more balanced and fair than most single-winner first-past-the-post elections. Parallel voting is mostly semi-proportional. Mixed system is the most proportional if the additional members are allocated in compensatory form.

There are many versions of MMP in use. Some use only a single vote; in some, voters cast two votes, one for a local candidate and one for a party. Some allocate compensatory seats to best losers; others allocate according to party lists. Some use levelling seats to compensate for potential overhang seats; others don't. Most impose an electoral threshold in order for a party to be eligible for any additional seats; some allow parties that elect one or more district seats to be eligible for additional seats even if its party share is below the threshold. Any barrier to access to the additional seats may produce wasted votes and dis-proportionality in the final result.

As well, there is single non-transferable vote, which is also semi-proportional. It has the advantage that parties play no direct role in elections and voters do not need to mark ranked votes. Each voter casts one vote for a candidate and as many candidates win by plurality as the number of seats in the district. Due to each voter casting just one vote, as in STV, and each district electing multiple members, as in STV, mixed representation is produced in each district and overall rough proportionality more or less. Without transferable votes, more votes are wasted than under STV.

Fairness

PR tries to resolve the unfairness of majoritarian and plurality voting systems where the largest parties receive an "unfair" seat bonus and smaller parties are disadvantaged, always under-represented, and on occasion win no representation at all (Duverger's law).^{[14][15][16]: 6–7} Under FPTP, an established party in UK elections has been elected to majority government with as little as 35% of votes (2005 UK general election). In certain Canadian elections, majority governments have been formed by parties with the support of under 40% of votes cast (2011 Canadian election, 2015 Canadian election). If turnout levels in the electorate are less than 60%, such outcomes allow a party to form a majority government by convincing as few as one quarter of the electorate to vote for it. In the 2005 UK election, for example, the Labour Party under Tony Blair won a comfortable parliamentary majority with the votes of only 21.6% of the total electorate.^[17]: 3 Such misrepresentation has been criticized as "no longer a question of 'fairness' but of elementary rights of citizens".^[18]: 22

However, intermediate PR systems with a high electoral threshold, or other features that reduce proportionality, are not necessarily much fairer: in the 2002 Turkish general election, using an open list system with a 10% threshold, 46% of votes were wasted.^[19]: 83 The other 54 percent of the votes did receive fair level of representation, though. Under first-past-the-post, a third or so of members are elected with less than half the votes cast in their district, the majority in such districts not getting any local representation and with no levelling seats getting no representation at all.

Plurality/majoritarian systems also benefit regional parties that win many seats in the region where they have a strong following but have little support nationally, while other parties with national support that is not concentrated in specific districts, like the Greens, win few or no seats. An example is the Bloc Québécois in Canada that won 52 seats in the 1993 federal election, all in Quebec, on 13.5% of the national vote, while the Progressive Conservatives collapsed to two seats on 16% spread nationally. The Conservative party although strong nationally had had very strong regional support in the West but in this election its supporters in the West turned to the Reform party (another regional party), which won all its seats west of Ontario, winning most of its seats west of Saskatchewan.^[16][20] Similarly, in the 2015 UK General Election, the Scottish National Party gained 56 seats, all in Scotland, with a 4.7% share of the national vote while the UK Independence Party, with 12.6%, gained only a single seat.^[21]

Representation of minor parties

The use of multiple-member districts enables a greater variety of candidates to be elected. It has been argued that in emerging democracies, inclusion of minorities in the legislature can be essential for social stability and to consolidate the democratic process.^[19]: 58

Critics, on the other hand, claim this can give extreme parties a foothold in parliament, sometimes cited as a cause for the collapse of the Weimar government. With very low thresholds, very small parties can act as "king-makers",^[22] holding larger parties to ransom during coalition discussions. The example of Israel is often quoted,^[19]: 59 but these problems can be limited, as in the modern German Bundestag, by the introduction of higher threshold limits for a party to gain parliamentary representation (which in turn increases the number of wasted votes).

Another criticism is that the dominant parties in plurality/majoritarian systems, often looked on as "coalitions" or as "broad churches",^[23] can fragment under PR as the election of candidates from smaller groups becomes possible. Israel, Brazil, and Italy (until 1993) are examples.^{[19]: 59, 89} However, research shows, in general, there is only a small increase in the number of parties in parliament (although small parties have larger representation) under PR.^[24]

Open list systems and STV, the only prominent PR system which does not require political parties,^[25] enable independent candidates to be elected. In Ireland, on average, about six independent candidates have been elected each parliament.^[26] This can lead to a situation where forming a Parliamentary majority requires support of one or more of these independent representatives. In some cases these independents have positions that are closely aligned with the governing party and it hardly matters. The Irish Government formed after the 2016 election even included independent representatives in the cabinet of a minority government. In others, the electoral platform is entirely local and addressing this is a price for support.

Coalitions

The election of smaller parties gives rise to one of the principal objections to PR systems, that they almost always result in coalition governments.^{[19]: 59 [11]}

Supporters of PR see coalitions as an advantage, forcing compromise between parties to form a coalition at the centre of the political spectrum, and so leading to continuity and stability. Opponents counter that with many policies compromise is not possible. Neither can many policies be easily positioned on the left-right spectrum (for example, the environment). So policies are horse-traded during coalition formation, with the consequence that voters have no way of knowing which policies will be pursued by the government they elect; voters have less influence on governments. Also, coalitions do not necessarily form at the centre, and small parties can have excessive influence, supplying a coalition with a majority only on condition that a policy or policies favoured by few voters is/are adopted. Most importantly, the ability of voters to vote a party in disfavour out of power is curtailed.^[11]

All these disadvantages, the PR opponents contend, are avoided by two-party plurality systems. Coalitions are rare; the two dominant parties necessarily compete at the centre for votes, so that governments are more reliably moderate; the strong opposition necessary for proper scrutiny of government is assured; and governments remain sensitive to public sentiment because they can be, and are, regularly voted out of power.^[11] However, this is not necessarily so; a two-party system can result in a "drift to extremes", hollowing out the centre,^[27] or, at least, in one party drifting to an extreme.^[28] The opponents of PR also contend that coalition governments created under PR are less stable, and elections are more frequent. Italy is an often-cited example with many governments composed of many different coalition partners. However, Italy is unusual in that both its houses can make a government fall, whereas other PR nations have either just one house or have one of their two houses be the core body supporting a government. Italy's current parallel voting system is not PR, so Italy is not an appropriate candidate for measuring the stability of PR.

Voter participation

Plurality systems usually result in single-party-majority government because generally fewer parties are elected in large numbers under FPTP compared to PR, and FPTP compresses politics to little more than two-party contests. Relatively few votes in a few of the most finely balanced districts, the "swing seats", are able to swing majority control in the house. Incumbents in less evenly divided districts are invulnerable to slight swings of political mood. In the UK, for example, about half the constituencies have always elected the same party since 1945;^[29] in the 2012 US House elections 45 districts (10% of all districts) were uncontested by one of the two dominant parties.^[30] Voters who know their preferred candidate will not win have little incentive to vote, and even if they do their votes have no effect, although they are still counted in the popular vote calculation.^[19]: 10

With PR, there are no "swing seats". Most votes contribute to the election of a candidate, so parties need to campaign in all districts, not just those where their support is strongest or where they perceive most advantage. This fact in turn encourages parties to be more responsive to voters, producing a more "balanced" ticket by nominating more women and minority candidates.^[16] On average about 8% more women are elected.^[24]

Since most votes count, there are fewer "wasted votes", so voters, aware that their vote can make a difference, are more likely to make the effort to vote, and less likely to vote tactically. Compared to countries with plurality electoral systems, voter turnout improves and the population is more involved in the political process.^[19][16][24] However, some experts argue that transitioning from plurality to PR only increases voter turnout in geographical areas associated with safe seats under the plurality system; turnout may decrease in areas formerly associated with swing seats.^[31]

Proportional systems show higher political efficacy, citizens' trust in their ability to influence and understand the government, compared to plurality and majoritarian systems.^[32]

Gerrymandering

First-past-the-post elections are dependent on the drawing of boundaries of their single-member districts, a process vulnerable to political interference (gerrymandering) even if districts are drawn in such a way as to ensure approximately equal representation. To compound the problem, boundaries have to be periodically re-drawn to accommodate population changes. Even apolitically drawn boundaries can unintentionally produce the effect of gerrymandering, reflecting naturally occurring concentrations.^[33]: 65

PR systems, due to having larger and fewer multiple-member districts, are less prone to gerrymandering  – research suggests five-seat districts or larger are immune to gerrymandering.^[33]: 66

Equality of size of multiple-member districts is not important (the number of seats can vary) so districts can be aligned with historical territories of varying sizes such as cities, counties, states or provinces. Later population changes can be accommodated by simply adjusting the number of representatives elected, without having to re-draw a single boundary. For example, Professor Mollison in his 2010 plan for STV for the UK divided the country into 143 districts and then allocated varying number of seats to each district (to add up to the existing total of 650 MPs) depending on the number of voters in each but with wide ranges (his five-seat districts include one with 327,000 voters and another with 382,000 voters). His district boundaries follow historical county and local authority boundaries, yet he achieves more uniform representation than does the Boundary Commission, the body responsible for balancing the UK's first-past-the-post constituency sizes.^[29][34]

Mixed member systems are susceptible to gerrymandering for the local seats that remain a part of such systems. Under parallel voting, a semi-proportional system, there is no compensation for the effects that such gerrymandering might have. Under MMP, the use of compensatory list seats makes gerrymandering less of an issue. However, its effectiveness in this regard depends upon the features of the system, including the size of the regional districts, the relative share of list seats in the total, and opportunities for collusion that might exist. A striking example of how the compensatory mechanism can be undermined can be seen in the 2014 Hungarian parliamentary election, where the leading party, Fidesz, combined gerrymandering and decoy lists, which resulted in a two-thirds parliamentary majority from a 45% vote.^[35][36] This illustrates how certain implementations of mixed systems (if non-compensatory or insufficiently compensatory) can produce moderately proportional outcomes, similar to parallel voting.

Link between constituent and representative

It is generally accepted that a particular advantage of plurality electoral systems such as first-past-the-post, or majoritarian electoral systems such as the alternative vote, is the geographic link between representatives and their constituents.^{[19]: 36 [37]: 65 [18]: 21} A notable disadvantage of PR is that, as its multiple-member districts are made larger, this link is weakened.^[19]: 82 In party list PR systems without delineated districts, such as the Netherlands and Israel, the there is no geographic link between representatives and their constituents. This makes it more difficult for local or regional issues to be addressed at the federal level. With relatively small multiple-member districts, in particular with STV, there are counter-arguments: about 90% of voters can consult a representative they voted for, someone whom they might think more sympathetic to their problem. In such cases it is sometimes argued that constituents and representatives have a closer link;^{[29][33]: 212} constituents have a choice of representative so they can consult one with particular expertise in the topic at issue.^{[33]: 212 [38]} With multiple-member districts, prominent candidates have more opportunity to be elected in their home constituencies, which they know and can represent authentically. There is less likely to be a strong incentive to parachute them into constituencies in which they are strangers and thus less than ideal representatives.^{[39]: 248–250} Mixed-member PR systems incorporate single-member districts to preserve the link between constituents and representatives.^[19]: 95 However, because up to half the parliamentary seats are list rather than district seats, the districts are necessarily up to twice as large as with a plurality/majoritarian system where all representatives serve single-member districts.^[18]: 32

An interesting case occurred in the Netherlands, when "out of the blue" a party for the elderly, the General Elderly Alliance gained six seats in the 1994 election. The other parties had not paid attention, but this made them aware. With the next election, the Party of the Elderly was gone, because the established parties had started to listen to the elderly. Today, a party for older folks, 50PLUS, has established itself in the Netherlands, albeit never with the same high number of seats. This can be seen as an example how geography in itself may not be a good enough reason to establish voting results around it and overturn all other particulars of the voting population. In a sense, voting in districts restricts the voters to a specific geography. Proportional voting follows the exact outcome of all the votes.^[40]

Potential lack of balance in presidential systems

In a presidential system, the president is chosen independently from the parliament. As a consequence, it is possible to have a divided government where a parliament and president have opposing views and may want to balance each other's influence. However, the proportional system favors government of coalitions of many smaller parties that require compromising and negotiating topics. As a consequence, these coalitions might have difficulties presenting a united front to counter presidential influence, leading to a lack of balance between these two powers. With a proportionally elected House, a President may strong-arm certain political issues

This issue does not happen in a parliamentary system, where the prime-minister is elected indirectly by the parliament itself. As a consequence, a divided government is impossible. Even if the political views change with time and the prime minister loses their support from parliament, they can be replaced with a motion of no confidence. Effectively, both measures make it impossible to create a divided government.

District magnitude

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

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

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

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.

Party-based systems

Candidate-based systems

Books

Journals