Editing Single transferable vote (section)

==Issues==
{{Main|Issues affecting the single transferable vote}}

===Degree of proportionality===
The degree of proportionality of STV election results depends directly on the district magnitude (i.e. the number of seats in each district). While Ireland originally had a median district magnitude of five (ranging from three to nine) in 1923, successive governments lowered this. Systematically lowering the number of representatives from a given district directly benefits larger parties at the expense of smaller ones.

Supposing that the [[Droop quota]] is used: in a nine-seat district, the Droop quota is 10% (plus one vote); in a three-seat district, it would be 25% (plus one vote). This electoral threshold seems significantly higher than for most party-list PR systems, based on percentage points. However, the Droop quota in a district covering just part of a jurisdiction may be set at as few votes as an list PR system's electoral threshold set at a lower percentage but based on the votes cast across a whole jurisdiction. For instance, in the [[2022 Danish election]], the main electoral threshold of 2 percent in use meant 71,000 of the 3.5{{nbsp}}million votes cast overall were required to be eligible for leveling seats, while in the 10-seat North Zealand Folketing constituency, the Droop quota (set at 9 percent) would have been 26,500 (1/11th of 292,000 valid votes). In the North Zealand constituency in the 2022 election, held using list PR (where the theoretical threshold is ten percent of district votes), the Conservative People's party{{snd}}with just 22,000 votes{{snd}}won one out of ten seats in the district. When levelling seats were allocated, the Independent Greens{{snd}}with almost 32,000 votes overall{{snd}}were not allocated any seats.<ref>{{Cite web| title=Fordelingen af mandater ved folketingsvalget den 1. november 2022 | language=da | trans-title=The distribution of seats in the general election on November 1, 2022 | url=https://www.dst.dk/valg/Valg1968094/other/Fordelingen-af-mandater-ved-FV2022.pdf | archive-url=https://web.archive.org/web/20221224044156/https://www.dst.dk/valg/Valg1968094/other/Fordelingen-af-mandater-ved-FV2022.pdf | archive-date=24 December 2022}}</ref>

An Irish parliamentary committee in 2010 discussed the "increasing trend towards the creation of three-seat constituencies in Ireland" and recommended not less than four-seat constituencies, except where the geographic size of such a constituency would be disproportionately large.{{sfn|Ireland|2010|p=177}} Establishing an acceptable geograpical district size is subjective; for example, the entire country of Ireland is smaller in size than each of the 18 largest single-member ridings used in Canadian elections and only a bit more than three times the size of the Scottish Highlands, which elects just one MP.<ref>https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=9810001001&lang=e Statistics Canada – Population and dwelling counts: Canada and federal electoral districts (2013 Representation Order)</ref>

STV provides proportionality by transferring votes to minimize waste, and therefore also minimizes the number of unrepresented or [[disenfranchised]] voters. As each winner is elected by exactly same number of votes as much as possible, each party receives approximately its due share of seats in each district and thus proportional representation overall.

=== Difficulty of implementation ===
A frequent concern about STV is its complexity compared with single-mark voting methods, such as [[plurality voting]] or [[party-list proportional representation]]. Before the advent of computers, this complexity made ballot-counting more difficult than in other methods, though Winnipeg used it to elect ten MLAs in seven elections (1920–1945).<ref>Monto, ''When Canada Had Proportional Representation'', p. 33</ref>

The algorithm is complicated, particularly if Gregory or another fractional-vote method is used. In large elections with many candidates, a computer may be required. (This is because after several rounds of counting, there may be many different categories of previously transferred votes, each with a different permutation of early preferences and thus each with a different carried-forward weighting, all of which have to be kept track of.)

===Role of political parties===
STV differs from other proportional representation systems in that candidates of one party can be elected on transfers from voters for other parties, a phenomenon sometimes referred to as vote ''leakage''.<ref name="Santucci2022">{{cite book |last=Santucci |first=Jack |title=More Parties or No Parties: The Politics of Electoral Reform in America |publisher=Oxford University Press |year=2022 |location=New York |isbn=978-0197630655}}</ref> Hence, STV may reduce the role of political parties in the electoral process and corresponding [[partisanship]] in the resulting government.

===By-elections===
As STV is a multi-member system and uses multi-member districts, filling a vacancy between elections can be problematic, and a variety of methods have been devised:
* The countback method is used in the [[Australian Capital Territory]], [[Tasmania]], Victoria, Malta, and [[Cambridge, Massachusetts]]. [[Casual vacancies]] can be filled by re-examining the ballot papers data from the previous election.<ref>{{Cite web |title=Do all countries have by-elections? Filling parliamentary vacancies around the world |url=https://www.electoral-reform.org.uk/do-all-countries-have-by-elections-filling-parliamentary-vacancies-around-the-world/ |access-date=23 June 2022 |website=www.electoral-reform.org.uk}}</ref> Officials determine the next-ranked candidate for those voters who supported the official whose seat was vacated.
* An alternative countback method is to appoint the candidate eliminated last (the most-popular unsuccessful candidate), who may represent a smaller minority than any of the candidates elected. Malta did this as a one-off for its [[2009 European Parliament election in Malta|2009 European elections]], to fill the prospective vacancy for the extra seat that arose from the [[Lisbon Treaty]].
* A head official or remaining members of the elected body appoint a new member to fulfill the vacancy. This may change the ideology of the seat.
* Hold a single-winner by-election (using instant-runoff voting); this allows each party to choose a new candidate and all voters across the wide district to participate. This is the method used in the Republic of Ireland in national elections and in Scotland's local elections. This likely produces a winner from the majority, which would be non-proportional if the seat was vacated by someone from a minority.
* The party of the vacant member nominates a successor, possibly subject to the approval of the voting population or the rest of the government. This is the method used in the Republic of Ireland in local elections.<ref>{{cite web |title=Local Elections Regulations, 1965. Section 87 |url=http://www.irishstatutebook.ie/eli/1965/si/128/made/en/print |website=S.I. No. 128/1965 – Local Elections Regulations, 1965.}}</ref>
* Officeholders create an ordered list of successors before leaving their seats. In the [[European Parliament]], a departing member from the Republic of Ireland or Northern Ireland is replaced with the top eligible name from a replacement list submitted by the candidate at the time of the original election. This method was also used in the [[Northern Ireland Assembly]] until 2009, when the practice was changed to allow political parties to nominate new MLAs in the event of vacancies. Independent MLAs may still draw up lists of potential replacements.<ref>{{cite press release |date=10 February 2009 |title=Change to the System for Filling Vacancies in the NI Assembly |url=http://www.nio.gov.uk/change-to-the-system-for-filling-vacancies-in-the-ni-assembly/media-detail.htm?newsID=15871 |publisher=Northern Ireland Office |access-date=5 October 2011 |url-status=dead |archive-url=https://web.archive.org/web/20120307065031/http://www.nio.gov.uk/change-to-the-system-for-filling-vacancies-in-the-ni-assembly/media-detail.htm?newsID=15871 |archive-date=7 March 2012}}</ref>

===Tactics===
{{See also|Tactical voting#Single transferable vote}}
If there are not enough candidates to represent one of the priorities the electorate vote for (such as a party), all of them may be elected in the early stages, with surplus votes being transferred to candidates with other views. On the other hand, putting up too many candidates might result in first-preference votes being spread too thinly among them, and consequently several potential winners with broad second-preference appeal may be eliminated before others are elected and their second-preference votes distributed. In practice, the majority of voters express preference for candidates from the same party in order,{{Citation needed|date=October 2010}} which minimizes the impact of this potential effect of STV.

The outcome of voting under STV is proportional within a single district to the varied opinions of voters, assuming voters have ranked their real preferences (marking their preferences to truly reflect their views). Due to the district voting mechanisms usually used in conjunction with STV, an election by STV does not guarantee proportionality across all districts. If proportionality is measured by looking at first-preference votes, the final result may appear disproportional. This is natural due to some votes being transferred from one party to another during the vote count procedure before all the seats are allocated.

In many elections, each party has their vote spread over the party's slate (if the party runs multiple candidates) so that the large parties' votes may be spread somewhat equally, and candidates of popular parties are mostly all more popular than candidates of less-popular parties. This happened in [[Cavan–Monaghan (Dáil constituency)|Cavan-Monaghan]] in the 2020 Irish general election, where Labour, PBP, Green and Aontu parties were the least popular. Their candidates were four of the five least-popular candidates in the first count and were eliminated quickly. SF, FG and FF parties were more popular{{Snd}}their candidates took the five seats{{Snd}}and candidates of those parties were already leading in the first count.<ref name="auto1">{{Cite web|url=https://data.oireachtas.ie/ie/oireachtas/electoralProcess/electionResults/dail/2020/2020-05-01_33rd-dail-general-election-results_en.pdf|title=33rd Dáil election results}}</ref>

Several methods of tactical or strategic voting can be used in STV elections but much less so than with first-past-the-post elections. In STV elections, most constituencies will be marginal, at least with regard to the allocation of a final seat. Manipulating STV requires knowledge of the contents of all the ballots, effectively only being possible after the ballots are counted; and discovering the correct votes to cast to manipulate the outcome strategically is [[NP-complete]].<ref>{{Cite web |url=https://courses.cs.duke.edu/fall06/cps296.2/stv_hard.pdf |title=Single Transferable Vote Resists Strategic Voting |access-date=27 February 2023}}</ref>

The difficulty of manipulating results under STV is credited with why it is chosen for use in part of the process of allocating the  [[Academy Awards]]. As part of the process of selecting winners for the Academy Awards, STV is used to choose nominees within each category. The Academy of Motion Picture Arts and Sciences claims that STV is preferred because "[a]lthough there are always instances in which an election procedure can be manipulated, an advantage of STV procedures is that the computations are too complex to be manipulated by a voter attempting to rank competitors of its most preferred candidate at the bottom of its preference list."<ref>{{Cite web |url=https://www.whydomath.org/node/voting/academy_awards.html |title=Why Do Math? |website=www.whydomath.org}}</ref>

STV satisfies the [[majority-rule principle]] in that the winners taken together are supported by a majority of the valid votes cast in the district. Variants like [[Schulze STV]] and [[CPO-STV]] also do.

===Elector confusion===
Critics{{who|date=November 2019}} contend that some voters find the mechanisms behind STV difficult to understand, but this does not make it more difficult for voters to rank the list of candidates in order of preference on an STV ballot paper (see {{section link||Balloting}}).{{sfn|Margetts|2003|p=68}}

STV systems vary, both in ballot design and in whether or not voters are obliged to provide a full list of preferences.

In jurisdictions such as Malta, Republic of Ireland and Northern Ireland, voters may rank as many or as few candidates as they wish. Consequently, voters sometimes, for example, rank only the candidates of a single party, or of their most preferred parties. Voters who do not fully understand the system may only vote for as many candidates as the instruction on the ballot gives before "and so on",<ref>{{Cite web |url=https://ballotbox.scot/le22-stv-1-2-3 |title=LE22: STV, it's only 1, 2, 3? |first=Ballot Box |last=Scotl |date=5 August 2022 |access-date=27 February 2023}}</ref> and may even "bullet vote", only expressing a first preference, or indicate a first preference for multiple candidates, especially when both STV and [[plurality voting system|plurality]] are being used in concurrent elections.{{sfn|Ombler|2006}}

Allowing voters to rank only as many candidates as they wish grants them greater freedom, but can also lead to some voters ranking so few candidates that their vote eventually becomes exhausted – that is, at a certain point during the count, it can no longer be transferred and influence the result. Some are non-transferable because the choices marked have already been elected, so the voter may be pleased with the overall election result even though their first preference was not elected and their vote itself was not used to elect anyone. Even if a voter marks many preferences, the vote may still be found to be non-transferable, if at any point the vote needs to be transferred and all the preferences ranked lower have already been eliminated or elected. But the number of non-transferable votes is fewer than the number of ignored votes under first-past-the-post and the number of effective votes, votes actually used to elect someone, is higher than under all but the most landslide first-past-the-post election contests.

The STV method may be confusing to some and may cause some people to vote incorrectly with respect to their actual preferences.

STV ballots can also be long; having multiple pages increases the chances of people not marking multiple preferences and thus missing later opportunities to have their vote transferred. After a vote is transferred twice, is at the end of the count and three candidates remain in the running for the last seat, the voter may have little interest in the choice. None of them were the voter's first choice, nor their second or third preference. And perhaps the voter has already seen one or two of their earlier choices already elected. Many votes up for transfer are found to be non-transferable in the last vote transfers. One to three members at the end are often elected with partial quotas, due to the number of exhausted votes. In STV elections, a majority of votes are used to elect the members who are elected.

===Other===
Some opponents{{who|date=April 2014}} argue that larger, multi-seat districts would require more campaign funds to reach the voters. Proponents{{who|date=October 2022}} argue that STV can lower campaign costs because like-minded candidates can share some expenses. Proponents reason that negative advertising is disincentivized in such a system, as its effect is diluted among a larger pool of candidates.

In addition, candidates do not have to secure the support of the largest voting block to be elected as under FPTP. STV ensures that each substantial group gets at least one seat, allowing candidates to focus campaign spending primarily on supportive voters. Under STV, it is not necessary to be the most popular candidate in the district to be elected; it is only necessary to have quota (or survive to the end when the remaining candidates are declared elected). To have quota, you do not need support from across the district necessarily. If a corner of the district has a quota worth of votes and the voters there support a candidate, that candidate will be elected and there is nothing the others elsewhere in the district can do about it. So, at least theoretically, you would not need to campaign across the district.<ref>Hoag, Effective Voting, (1914)</ref>

The larger, multi-member constituencies can result in less, rather than more, representation of local communities within the electoral district. The representatives could potentially all be from one part of the region, leaving other communities without representation.

Furthermore, STV requires multi-member districts (MMDs). It is thus impossible to use MMDs in the Scottish Highlands to elect member of the UK Parliament because only one member is elected in that area.<ref>{{Cite web |url=https://ukchristianparty.org/where-are-you/scotland/ |title=Scotland |access-date=18 December 2022 |archive-date=19 August 2022 |archive-url=https://web.archive.org/web/20220819013610/https://ukchristianparty.org/where-are-you/scotland/ |url-status=dead }}</ref> To create an MMD in a sparsely-settled area, an electoral district would have to cover a large area just to capture the required population to be represented by multiple members. There can be a greater disconnect between the voter, or community, and their representatives. If areas with low population density were using multi-member districts to elect the relatively few high-level members of Parliament in Scotland or of the UK Parliament, constituencies could become so large as to seem to be impractical.<ref>{{cite web |date=18 June 2013 |title=Advantages and Disadvantages of Using the Single Transferable Vote System |url=https://www.uk-engage.org/2013/06/what-are-the-advantages-and-disadvantages-of-using-the-single-transferable-vote-stv-system/ |access-date=3 June 2022 |website=UK Engage}}</ref> However, Scotland successfully uses multiple-member regions in its Scottish Parliament elections and STV in its Local Authority elections. The large number of Local Authority or Scottish Parliament members allows the creation of MMDs without having each district cover too large an area.<ref>{{Cite web |url=https://www.scotland.org/live-in-scotland/where-to-live-in-scotland/the-highlands |title=The Highlands &#124; Scotland.org |website=Scotland |access-date=27 February 2023}}</ref> Meanwhile, MMDs even of immense size can be used successfully. In New South Wales, Australia, the whole state elects 21 members of the upper house in one single STV contest and has done so since 1991.<ref>"Legislative Council – State Election 2019". vtr.elections.nsw.gov.au. Archived from the original on 26 March 2019. Retrieved 26 March 2019</ref>