- Where needed, I’ve tried only to clarify and simplify the important content offered by the existing article. At the same time, I see the existing article as longer than it should be because parts of it currently has simply copied whole, or parts, of other relevant main articles. Links to this relevant information are retained in this shortened-proposed revision. Please offer me any guidance or constructive criticisms you may have in mind so your improvements can also be added before my planned attempt to publish a revision after June 7, 2023:
- Not to be confused with Instant-runoff voting.
- Simplified example of an STV ballot
- Part of the Politics series
- Electoral systems
- Single-winner/majoritarian
- Proportional representation
- Mixed systems
- Other systems and related theory
- Politics portal
- Single transferable vote
- Single transferable vote (STV) elects a number of candidates at the same time. It is used to elect many local councils and state legislative bodies in the US, UK, Australia, and Malta. In the US, STV is usually called proportional ranked-choice voting (PRCV), but sometimes also preferential voting, preference voting, choice voting, multi-winner ranked-choice voting.
- Advocates for STV argue it is an improvement over winner-take-all non-proportional voting systems such as plurality voting (First-Past-The-Post (FPTP)), where vote splits commonly result in a majority of voters electing no one and the successful candidates having support from just a minority of the voters. In most cases, STV prevents one party taking all the seats by giving a larger range of candidates a realistic chance of being elected.
- STV is the system of choice of the Proportional Representation Society of Australia (which calls it quota-preferential proportional representation), of the Electoral Reform Society in the United Kingdom, and of FairVote in the United States (PRCV).
- With STV, each voter casts a single vote by ranking the candidates as first, second, third preference, etc. Consequently, many more voters are represented, and more proportionally than is achieved with traditional plurality voting (FPTP). Voters have the option to rank the candidates so that their vote may be transferred according to the preferences marked on their ballot. If an STV voter’s first preference candidate has not received enough votes to be elected, perhaps their second, third, or later preference candidate will be elected.
- Under STV, no one party or voting bloc can take all the seats in a multi-winner district unless the number of seats in the district is very small, or almost all the votes cast are cast for one party's candidates, which is seldom the case. This makes it different from other multi-member district-voting systems. In plurality systems (FPTP), one party or a voting bloc can take all the seats in a district. Under STV, every sizable group within the district wins at least one seat. The more seats the district has, the smaller fraction of the electorate needed to elect a member. Minority factions have a better chance to be represented. In this way, STV provides some proportional representation. Consequently, STV reduces the number of "wasted" votes. An important characteristic of STV is that it enables citizens to choose to vote for individual candidates rather than parties. Voters can create their own ordered list of candidates.
- The way STV votes are counted to "waste" as few votes as possible is described below.
- STV’s count
- The STV count starts by calculating the smallest total number of votes that each of the candidates must receive to be elected, and to exclude the possibility of any additional candidate being elected by the remaining votes not countable for any of the winners. This smallest number is called the quota.
- For example, the Droop quota is equal to one vote more than the quotient resulting from dividing the total number of ballots cast (the dividend) by one more than the target number of winners: Droop quota = 1 + [number of ballots/number of winners + 1].
- For simplicity, consider below an STV election for a seven-member electoral district. Therefore, when electing these seven members, the divisor is 8.
- In the first round of the count, the total number of first preferences awarded to each candidate by all the ballots is recorded. If any candidate’s total is equal to or larger than the quota, they are elected. If any of these elected candidates has received more than the quota number of votes, the surplus number of votes received by this winner are transferred to the candidate next preferred on each of all the ballots initially received by this winner.
- To treat all ballots equally, the winner retains only the fraction of each of these ballots that together provides this winner with the required quota for their election. The fraction not retained is transferred to the next preferred candidate on each ballot when available.
- Next, after all these relevant fractions are transferred to each next preferred candidate, any other candidate who now has at least the quota is also elected. Again, any surplus fractions received by this next winner are also similarly transferred to other relevant next-preference candidates. This process is repeated until all the surplus votes from all these winners have been transferred to next-preferred candidates.
- If the target number of candidates to be elected has not yet been elected, the candidate who received the fewest first preferences is eliminated, and all the ballots they received are transferred to the next preference candidate on each of their ballots when available. This eliminating and transferring process continues until the required number of candidates has been elected.
- If any of the ballots initially held by losing candidates did not also prefer any winning candidate, these ballots are “non-transferable” and said to be “exhausted.” The vote in each of these ballots is "wasted."
- This can also mean that one or several of the last number of candidates to be elected has unavoidably not received the full quota. However, each such winner among the target number of seven council members has at least received the largest number of votes available at that closing stage of the count.
- Terminology
- In this article, "STV" refers only to preferential votes cast in multi-seat districts (e.g. PR-STV or STV-PR in Scotland). Hare–Clark is the name given to PR-STV elections in Tasmania and the Australian Capital Territory.[2][3]
- When preferential votes are similarly used but only for single-winner elections, the method is usually called "ranked-choice voting" RCV) in the US, and instant-runoff voting (IRV) or alternative vote (AV) in the UK. These ballots are counted somewhat differently to ensure that the winner will have been supported by the largest possible plurality. Instant-runoff voting (IRV) is the single-winner analogue of STV. Consequently, it is sometimes referred to as "single-winner ranked-choice voting". Its goal is to represent a majority of the voters in a district by a single official, as opposed to STV's goal of representing a majority of voters by electing multiple officials somewhat proportionally from the substantial voting blocks in a district.
- Below, many examples and varieties of STV are described, compared, discussed, and a history of STV presented.
- STV example
- Suppose an election is conducted to determine what three foods to serve at a party. There are seven choices: Oranges, Pears, Strawberries, Cake (Strawberry-chocolate), Chocolate, Hamburgers and Chicken. Only three of these may be served.
- There are 23 guests, and the hope is that each guest will be served at least one food that they are happy with. It is decided to use STV to make the decision. Each guest is given one vote but is also allowed to cast two optional alternate preferences to be used only if the first preference cannot select a food or to direct transfer of surplus votes if it does. The 23 guests at the party mark their ballots: some mark first, second and third preferences; some mark fewer preferences. When the ballots are counted, it is found that the ballots are marked in seven distinct combinations, as shown in the table below:
- 1st preference
- 2nd preference
- 3rd preference
- of ballots
- 4
- 7
- 1
- 3
- 1
- 4
- 3
- The table is read as columns: the left-most column shows that there were four ballots with Orange as the first choice, and Pear as second; while the rightmost column shows there were three ballots with Chicken as first choice and Hamburger second.
- The election step-by-step:
- Step
- Votes for each option
- Setting the quota
- The quota is 6
- Step 1
- 4
- 7
- ELECTED
- (1 surplus vote)
- 1
- 3
- 1
- 4
- 3
- Step 2
- 4
- ELECTED
- 1 + 1 = 2
- 3
- 1
- 4
- 3
- Step 3
- 4
- ELECTED
- 2
- 3 + 1 = 4
- eliminated
- 4
- 3
- Step 4
- 4
- ELECTED
- eliminated
- 4 + 2 = 6
- ELECTED
- (0 surplus votes)
- eliminated
- 4
- 3
- Step 5
- 4
- ELECTED
- eliminated
- ELECTED
- eliminated
- 4 + 3 = 7
- ELECTED
- (1 surplus vote)
- eliminated
- Result
- ELECTED
- ELECTED
- ELECTED
- A Sankey chart illustrating the vote process
- Setting the quota: The Droop quota formula is used, giving Quota = total votes / (options to choose + 1) + 1, rounded down = 23 / (3 +1) + 1 rounded down = 6.75 rounded down = 6
- Step 1: First-preference votes are counted. Pears reaches the quota with 7 votes, and is therefore elected on the first count, with 1 surplus vote. All of the voters who gave first preference to Pears preferred Strawberry next, so the surplus vote is awarded to Strawberry.
- Step 2: No other option has reached the quota, and there are still two to elect with six options in the race, so elimination of lower-scoring options starts. Chocolate has the least votes and is eliminated. According to their only voter's next preference, this vote is transferred to Cake. No option has reached the quota, and there are still two to elect with five in the race, so elimination of options will continue next round.
- Step 3: Of the remaining options, Strawberry now has the least votes and is eliminated. In accordance to the preferences of both the only voter who voted Strawberry, and the Pear–Strawberry–Cake vote, these votes are transferred to Cake.
- Step 4: Cake reaches the quota and is elected. No other option has reached the quota, and there is still one to elect with three in the race, so elimination of options will continue next round.
- Step 5: Chicken has the least votes and is eliminated. According to the Chicken voters' next preference, this vote is transferred to Hamburgers.
- Step 6: Hamburgers is elected with 7 votes in total. Hamburgers now also has a surplus vote, but this does not matter, since the election is over. There are no more foods needing to be chosen – three have been chosen. Orange ends up being neither elected nor eliminated.
- Result: The winners are Pears, Cake, and Hamburgers.
- STV in this case produced a higher number of effective votes – 19 votes were used to elect the successful candidates. (Only the votes placed for Oranges were neither used to select a food nor transferred.) As well, there was general satisfaction with the choices selected – 14 voters saw their first preference chosen, and the 9 others saw their second preference chosen. In addition, seven saw their first and third choices selected; one saw his second and third choice selected.
- Note that if Hamburger had received only one vote when Chicken was eliminated, it still would have won because the only other remaining candidate, Oranges, has fewer votes so would have been declared defeated in the next round. This would have left Hamburger as the last remaining candidate to fill the last open seat, even if it did not have quota.
- This count compared to other systems
- This result differs from the one that would have occurred if the voting system used had been non-PR, such as single non-transferable vote (SNTV), first-past-the-post (FPTP) in three districts, first-past-the-post at-large group ticket voting as used to elect members of the U.S. electoral college, or a single-winner plurality system in three districts.
- Single non-transferable vote results would have had Orange among the three winners, as opposed to Cake, for having a greater number of first-preference votes. Under SNTV, 15 voters would have seen their first preference win (Oranges, Pears and Hamburgers); only 3 voters would have not seen their first preference food served but would have seen their 2nd preference food served. Five voters would not be served any of their favourites.
- Under plurality, the guests would have been split into three groups with one food chosen by each group based on just the most popular food in each group. The result in this case would have been dependent on how the groups are formed (gerrymandering of the groups to bias the election toward a particular result could also occur). It might have been Strawberry donuts, Pears and Hamburgers, but also the foods chosen might have been Pears in two groups (districts) and Hamburgers in the other. Or even just Pears alone might have won in each of the three "districts", in which case only 7 guests out of 23 would have seen their first choice served, a very unrepresentative outcome, given that three different foods could have been served.
- Similar problems arise to a lesser degree if all districts use a majority system instead of plurality (for instance, two-round or instant-runoff voting) as at least in all districts the majority would have been quite happy, but that still leaves the minority unrepresented. Note that so-called “majority systems” elect the plurality candidate if neither “two-round” or “instant-runoff” voting identify a candidate supported by a majority.
- It could happen under any three-district single-winner system that none of the groups elect Pears, if the 7 votes for it are split and in each "district" there is another food that beats it (e.g. Oranges, Hamburgers and Chicken).
- If the voters had been able to choose only one food to serve (as in plurality, but without "districts"), it is likely that Pears, the choice of less than a third of the 23 party-goers, would have won, meaning Pears would be the only food served at the party. Even if they held two rounds of voting, the bare majority that prefers some kind of fruit (Oranges, Pears, Strawberries) would have dominated all other choices.
- Giving electors a single transferable vote is very different from simply giving each voter more votes to cast. Plurality block voting is such a system. Under it, each voter is given as many votes as there can be winners. This system can produce very unrepresentative results. In the example above, if every voter could vote for three options, the small majority of voters who chose a fruit could easily force all three outcomes to be fruit of some kind: an outcome that is unlikely to be more representative than simply choosing only one winner. In an extreme example, where no faction can command an absolute majority, the largest of the minority groups can force a one-outcome result by running clone candidates. For example, the seven supporters of Pears could arrange in advance to have three types of Pears included on the ballot, then vote for all three, and if no other option reaches more than 7 votes, all three foods would be a type of Pear. The only way this could be avoided would be for those who do not want Pears to vote tactically by not choosing their preferred option, but instead whatever they consider to be the least bad outcome that is still likely to gain the required number of votes.
- Example for an election with parties
- Elections with parties are conducted in very similar manner to the non-partisan STV election presented above. Parties need not play any role in STV elections – each voter marks preferences for individual candidates and his or her secondary preferences may cross party lines if so desired.
- This example shows election of five members in a district. Party A runs five candidates, Party B runs three, and there is one independent in the race. The election is conducted under STV with the Hare quota, which for five seats is 20% (100% divided by five).
- First round
- Candidate
- Party
- Votes
- (first preferences)
- Quota
- Elected?
- If elected: surplus votes
- Candidate A1
- Party A
- 1%
- 20%
- Candidate A2
- Party A
- 9%
- Candidate A3
- Party A
- 25%
- Yes
- 5%
- Candidate A4
- Party A
- 8%
- Candidate A5
- Party A
- 5%
- Candidate I
- Independent
- 7%
- Candidate B1
- Party B
- 11%
- Candidate B2
- Party B
- 18%
- Candidate B3
- Party B
- 16%
- TOTAL
- 100%
- In the first round, the vote tally of the most popular candidate of Party A, Candidate A3, is more than quota, so they win a seat.
- Second, third and fourth rounds
- Surplus votes are distributed; the voters of Candidate A3 have put another politician from their party as their second preference, Candidate A4, so A4 now receives Candidate A3's surplus votes. This transfer of 5 percent of the votes leaves A3 with the quota (20 percent) and leaves A4 with 13 percent.
- In the third and fourth rounds, the least popular candidates are eliminated (Candidates A1 and A5) and their votes transferred to their next preferences. Voters of Candidate A5 are not very partisan, they actually prefer the independent candidate over the other candidates of Party A still in the race.
- Candidate
- Party
- Votes
- Quota
- Elected?
- If elected: surplus votes
- Party A
- 1% − 1% = 0%
- 20%
- Candidate A2
- Party A
- 9% + 1% = 10%
- Candidate A3
- Party A
- 25% − 5% = 20%
- Yes
- already elected
- Candidate A4
- Party A
- 8% + 5% = 13%
- Party A
- 5% − 5% = 0%
- Candidate I
- Independent
- 7% + 5% = 12%
- Candidate B1
- Party B
- 11%
- Candidate B2
- Party B
- 18%
- Candidate B3
- Party B
- 16%
- TOTAL
- 80% (1 already elected)
- Fifth and sixth rounds
- In the fifth round, Candidate A2 is eliminated with all their votes going to the candidate A4, the last remaining candidate from Party A, who is elected. The surplus votes of Candidate A4 are transferred. All the voters who helped elect Candidate A4 prefer the independent candidate to the candidates of the other party so their 3% surplus votes will go to Candidate I in the sixth round.
- Candidate
- Party
- Votes
- Quota
- Elected?
- If elected: surplus votes
- Party A
- 20%
- Party A
- 10% − 10% = 0%
- Candidate A3
- Party A
- already elected
- Yes
- Candidate A4
- Party A
- 13% + 10% = 23%
- Yes
- 3%
- Party A
- Candidate I
- Independent
- 12% + 3% = 15%
- Candidate B1
- Party B
- 11%
- Candidate B2
- Party B
- 18%
- Candidate B3
- Party B
- 16%
- TOTAL
- 80% (1 already elected)
- Seventh round
- There are now only four candidates remaining and three seats remaining open. The least popular candidate (Candidate B1) is declared defeated. There are now only three candidates in the race, so they are automatically declared elected regardless of whether they reached the quota. These three have received the three largest number of remaining votes. The count ends there when the last seats are declared filled.
- No ballots would be wasted in the improbable even the the rankings on the 11 ballots received by eliminated Candidate B1 could be transferred to supply Candidates A3 and A4 with more votes as suggested below.
- Candidate
- Party
- Votes
- Quota
- Elected?
- If elected: surplus votes
- Party A
- 20%
- Party A
- Candidate A3
- Party A
- already elected
- Yes
- Candidate A4
- Party A
- already elected
- Yes
- Party A
- Candidate I
- Independent
- 15% + 5% = 20%
- Yes
- Party B
- 11% − 11% = 0%
- Candidate B2
- Party B
- 18% + 6% = 24%
- Yes
- Candidate B3
- Party B
- 16%
- Yes
- TOTAL
- 60% (2 already elected)
- Under STV, candidates A3, A4, I, B2 and B3 were elected.
- This vote count varies from the reality of many STV systems because there were no "exhausted" non-transferable votes. In most real-life STV elections, some votes that are set to be transferred cannot be and the number of votes still in play at the end is lower than the number of votes cast and counted in the 1st round. As well, the Droop quota is usually used in real-life STV elections. With the Droop quota in effect and five seats, it would have taken 17 percent to be elected with quota, not 20 percent as under the Hare quota.
- In this case, as in all STV elections, about 80 percent or more of the votes were used to actually elect someone. A majority of the members elected in the district represent the sentiments of a majority of the voters.
- Compared to other systems
- This result differs from the one that would have occurred if the voting system used had been non-PR, such as single non-transferable vote (SNTV), plurality (FPTP) in five districts, plurality at-large general ticket voting (as used to elect members of the U.S. electoral college), or a single-winner majoritarian system in five districts
- This result is different than if all voters could only vote for their first preference but still all seats were filled in a single contest, which is called the single non-transferable vote. Single non-transferable vote (SNTV) is used in Japan. With SNTV, each voter can only express their first preference. A degree of proportional representation can only be achieved with SNTV if each party coordinates its supporters to vote strategically – different groups to vote for a different designated party candidate.
- Under SNTV, the above five candidates would be most popular only if the relevant first preferences were considered for candidates A2, A3, B1, B2 and B3. This means even though Party B's candidates had less support together, they would have received 60% of seats, and Party A only 40%. In this case, Party A overextended themselves by fielding too many candidates, but even if they had strategically nominated only three, they would not necessarily have been successful in gaining three seats instead of two seats, because one or two of their candidates might have taken the lion share of their party votes, leaving not enough votes for the other(s) to be elected. This could be addressed under SNTV if the party voters used coordinated strategic voting.
- If voters could vote for five candidates (but not cast ranked votes) – ) as under the plurality block voting system, a type of multiple non-transferable vote – , Party A could have won all seats, leaving Party B and voters of the independent candidate without representation. This is because if all voters of Party A voted for all five of the Party A candidates, every Party A candidate would have been among the five candidates with the most votes and would have been declared elected. That would have meant that Party A with support of only 48 percent of voters would have had all the representation.
- Under majority block voting, if voters voted along party lines, every Party A candidate would have received a vote from 48 percent of the voters, and some even up to 55% if voters of Candidate I also voted for some Party A candidates with their 4 other votes. At the same time, Party B's candidates could only get up to 52% of the votes with the same tactics. If the voters are partisan enough, the likely outcome is that party A would take all the seats although Party A took less than half the votes (minority representation) and all other votes are wasted.
- In single-winner systems, whether plurality (FPTP) or majoritarian, the outcome is uncertain. It likely would be that Party A with 48 percent of the votes might achieve a clean sweep of all five seats or easily Party A might take four of the five with Party B taking just one. (The first case would have been achieved by Party B votes being “cracked” split between districts in which their votes will be less effective; the second case would have been achieved by Party B voters being mostly “packed” into just one district, leaving Party A with easy victories in the other four districts.) On the other hand if districts were drawn in a different way, Party A and Party B might have divided the seats in a three to two ratio. Even under certain circumstances, the Independent candidate might take a seat if their supporters are sufficiently concentrated in one district.
- STV election results are roughly proportional (to the extent the number of seats allows) and take into account more than the first preferences of voters. Under STV (as seen in the example above), when it comes to secondary preferences, some voters who like a candidate from a certain party best might prefer an independent (or even a rival party candidate) before other candidates of their first choice's party. This means that even if it seems that some faction (based on first preferences) is over-represented or under-represented in the outcome, the outcome actually closely adheres to a combination of the first preferences of many voters and secondary preferences of most of the other voters. Under STV, about 80 percent of voters see their vote actually used to elect someone they prefer (and even more than that portion see someone they prefer elected even if their vote itself was not used to elect anyone), while under FPTP, often less than half of the votes are used to elect anyone and only the largest group in each district is represented.
- Party
- Popular vote
- STV – Hare quota
- SNTV
- Plurality block voting
- Party-list PR
- %
- Seats
- %
- Seats
- %
- Seats
- %
- Seats
- %
- Party A
- 48%
- 2
- 40%
- 2
- 40%
- 5
- 100%
- 3
- 60%
- Party B
- 45%
- 2
- 40%
- 3
- 60%
- 0
- 0%
- 2
- 40%
- Independent
- 7%
- 1
- 20%
- 0
- 0%
- 0
- 0%
- 0
- 0%
- Other versions of STV
- In sharp contrast to all the other versions of STV described above and below, the following iteration called evaluative proportional representation (EPR) wastes no votes. With EPR, voters rank candidates instead by grading them as either Excellent, Very Good, Good, Acceptable, Poor, or Reject. These grades allow voters more clearly to express the value judgments that led them to rank the candidates differently on their ballot. Unlike most other forms of STV in use, EPR voters can give the same ranking (grade) to more than one candidate. All the grades are counted to ensure that each voter’s ballot equally increases the voting power of the elected candidate to whom they have awarded their highest available grade. Each elected candidate has a different weighted vote in the legislative body exactly equal to the number of ballots exclusively counted for them. No citizen’s vote is wasted quantitatively or qualitatively.
- The spare vote is a version of single transferable voting applied to the ranking of parties, first proposed for elections in Germany in 2013. The spare vote system includes the step of transferring the votes of eliminated choices to the next-indicated choice of party, but it does not transfer surplus votes.
- The mixed ballot transferable vote (MBTV) is a mixed version of STV, where voters may rank both candidates and parties, even both interchangeably, depending on the ballot type, but must choose at least a local (district) candidate (1st preference) and a national list (2nd preference). The list preferences are used if the vote is unused in the district election, which may use FPTP, IRV or STV rules; in the STV case, the vote is transferred to another tier in favour of the chosen party list. (This is in contrast to the mixed single vote, which is currently used in Hungary, where voters may not define a separate party-list preference and do not cast preferential votes.)
- Indirect single transferable voting is a non-ranked-vote version of STV. Single voting in a multi-seat district is retained. Voters do not mark their ballots with rankings, but votes are transferred, as needed, based on the eliminated or elected candidate's pre-set instructions. This is a useful system to achieve many of the benefits of STV in districts where it is difficult to collect all the ballots in one central place to conduct STV transfers or where X voting is preferred over ranked voting due to voters' inability or disinterest in ranking candidates. Once known as the Gove system, or the schedule system of PR, it was invented by Massachusetts legislator William H. Gove of Salem and Archibald E. Dobbs of Ireland, author of Representative Reform for Ireland (1879). (STV with group ticket Voting also conducts transfers without reference to alternate preferences marked by voters.) In 1884, Charles L. Dodgson (Lewis Caroll) argued for a proportional representation system based on multi-member districts similar to indirect STV, with each voter casting only a single vote, quotas as minimum requirements to take seats, and votes transferable by candidates through what is now called liquid democracy. The difference from "indirect STV" is that under liquid democracy, candidates and members may transfer votes after the votes are cast to build coalitions; they do not have to publish their list beforehand.
- The modified d'Hondt electoral system is a variant of STV, where an electoral threshold for parties is applied.
- Two-vote MMP and additional member system systems may also be interpreted as a related, effectively preferential mixed system. Votes are not transferred, but a voter may vote differently for the local election and the overall party vote, with one, both or neither of those votes electing someone.[citation needed]
- Sequential proportional approval voting is similar to STV in transferring votes and resulting in proportional representation, while in contrast to STV utilizes approval instead of ranking on the ballot.
- See: Main article: Counting single transferable votes
- Issues
- Main article: Issues affecting the single transferable vote
- Degree that results are proportional
- The degree that the results of an STV election are proportional depends importantly on 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 quota or threshold is 10% (plus one vote); in a three-seat district, it would be 25% (plus one vote). This electoral threshold is significantly higher than for most party-list PR systems.
- A parliamentary committee in 2010 discussed the "increasing trend towards the creation of three-seat constituencies in Ireland" and recommended not less than four-seaters, except where the geographic size of such a constituency would be disproportionately large.[63]
- STV tries to provide proportional results by transferring votes to minimise waste, and therefore also minimises the number of unrepresented or disenfranchised voters.
- Difficulty of implementation
- A frequent concern about STV is its complexity compared with single-mark voting methods, such as plurality voting or closed 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-member legislative assemblies (MLAs) in seven elections (1920–1945).[5]
- The algorithm is complicated, particularly if Gregory, Meek, or another fractional-vote method is used ( Main article: Counting single transferable votes). 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 preferences being transferred, each with a different carried-forward weighting, all of which have to be kept track of.)
- By-elections
- As STV is a multi-member system, filling vacancies 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.[6]
- • Another option is to have a head official or remaining members of the elected body appoint a new member to fulfill the vacancy.
- • A third way to fill a vacancy is to hold a single-winner by-election (effectively instant runoff); this allows each party to choose a new candidate and all voters to participate. This is the method used in the Republic of Ireland in national elections, and in Scotland's local elections.
- • Yet another option is to allow the party of the vacant member to nominate 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.[7]
- • Another possibility is to have the candidates themselves 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.[8]
- • For its 2009 European elections, Malta introduced a one-off policy to elect the candidate eliminated last to fill the prospective vacancy for the extra seat that arose from the Lisbon Treaty.
- Tactics
- See: Tactical voting § Single transferable vote
- If a large section of the electorate discovers that not enough candidates are available to represent their highest priority concern, the available smaller number are likely to be elected in the early stages of the count, but with some of their 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] which minimises the impact of this potential effect of STV.
- The outcome of voting under STV is nearly proportional within a single election to the collective preference of voters, assuming voters have ranked their real preferences. Due to other voting mechanisms usually used in conjunction with STV, such as a district or constituency system, an election by STV is likely to provide less proportional results across all districts. If proportions are measured by looking at first preference votes, the final result may not be as proportional due to some votes being transferred to other candidates later in the count.
- Accordingly, in many elections, each party has their vote spread over the party's slate (if the party runs multiple candidates so that all the large parties' votes are spread somewhat equally), and candidates of popular parties are mostly all more popular than candidates of less-popular parties. This happened in 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 – their candidates took the five seats – and candidates of those parties were already leading in the first count.[9]
- A number of methods of tactical or strategic voting exist that can be used in STV elections but much less so than with plurality 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 effectively impossible (NP-complete).[10]
- The difficulty of manipulating results under STV is credited with why it is chosen for use in part of the process of allocating 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."[11]
- While STV generally does not satisfy the Condorcet criterion, Condorcet method variants like Schulze STV and CPO-STV do.
- Elector confusion
- Critics [who?] contend that some voters find the way the STV ballots are counted too 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 §Voting).[71]
- 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",[12] and may even "bullet vote", only expressing a first preference, or indicate a first preference for multiple candidates, especially when both STV and plurality are being used in concurrent elections.[73]
- 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 plurality and the number of effective votes, votes actually used to elect someone, is higher than under all but the most landslide plurality election contests.
- The STV method may be confusing to some and may cause some people to vote incorrectly with respect to their actual preferences.
- Other considerations
- Some opponents [who?] argue that larger, multi-seat districts would require more campaign funds to reach the voters. Proponents [who?] argue that STV can lower campaign costs because like-minded candidates can share some expenses. Proponents reason that negative advertising is disincentivised 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 multi-member district (MMDs) to be elected; it is only necessary to have the quota (or survive to the end when some remaining candidates may be declared elected). To have the quota, you do not necessarily need support from across the district. 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.[13]
- The larger, multi-member constituencies can result in less, rather than more, representation of some 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 cannot be used in the large geographical area of the Scottish Highlands because only one member is elected to the UK Parliament from that small population.[14] To create an MMD in a sparsely-settled area, an electoral district would have to cover even a larger area just to capture the required population to be represented by multiple members. There can be a greater disconnect between a voter, or a community, and their official 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.[15] Still, 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.[16] 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.[17]
- 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. 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. 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. 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.
- Analysis of results
- Academic analysis of voting systems such as STV generally centres on the voting system criteria that they pass. No preference voting system satisfies all the criteria in Arrow's impossibility theorem: in particular, STV fails to achieve independence of irrelevant alternatives (like most other vote-based ordering systems) and monotonicity.
- Migration of preferences
- The relative performance of political parties in STV systems is sometimes analysed in a different fashion from that used in other electoral schemes. For example, seeing which candidates are declared elected on first-preference votes alone in the 2012 Scottish local elections, where 1223 members were elected, can be shown as follows:
- 2012 Scottish local elections
- Party
- Total elected
- Elected on 1st prefs alone
- Total
- %
- % (2007)
- Conservative
- 115
- 46
- 40
- 41
- Labour
- 394
- 199
- 51
- 37
- Liberal Democrats
- 71
- 20
- 28
- 22
- SNP
- 425
- 185
- 44
- 57
- Green
- 14
- 1
- 7
- –
- Independent
- 200
- 79
- 40
- 32
- Other
- 4
- 2
- 50
- 14
- Totals
- 1,223
- 532
- 44
- 40
- The data can also be analysed to find the proportion of voters who express only a single preference, or those who express a minimum number of preferences, to assess party strength. Where parties nominate multiple candidates in an electoral district, analysis can also be done to assess their relative strength.
- Other useful information can be found by analysing terminal transfers—i.e., when the votes of a candidate are transferred and no other candidate from that party remains in the count—especially with respect to the first instance in which that occurs:
- Average first terminal transfer rates (2012)
- Transferred from
- % non-transferable
- % transferred to
- Con
- Lab
- LD
- SNP
- Ind/Other
- Conservative
- 34
- –
- 8
- 32
- 8
- 18
- Labour
- 48
- 6
- –
- 13
- 17
- 17
- Liberal Democrats
- 23
- 22
- 20
- –
- 16
- 19
- SNP
- 44
- 6
- 18
- 14
- –
- 18
- Green
- 20
- 5
- 19
- 20
- 18
- 17
- The transfers of votes under STV mean that candidates who did well on first-preference votes in the first count (but not well enough to be immediately declared elected) may not be elected in the end, and those who did poorly on the first count may be elected in the end. This is due to transfers made according to second and later preferences. This can also be analysed, again using the 1223 members elected in the Scottish local elections. Some of the leading candidates in the first count were not elected but, comparing the number to the total number of members elected in these elections, the successful candidates were mostly set in the first count (through the simple mechanics of single voting in multi-member districts), before any vote transfers are done. Only about ten percent or less of the front runners in the first count were not elected in the end.
- Only 68 of the elected members, of the overall 1,223 successful candidates, were not already in a winning position in the first count, thus mostly showing that vote transfers usually put a polish on the first-count ranking of candidates established through single voting in multi-seat districts.
- Candidates not in a winning position on 1st preference who secured election, by party (2012).
- Political party
- Elected though
- not in
- top 3 or 4
- Not elected
- though in
- top 3 or 4
- Net gain/loss
- 2012
- 2007
- Conservative
- 1
- 16
- −15
- −24
- Labour
- 21
- 8
- +13
- −17
- Liberal Democrats
- 4
- 3
- +1
- +29
- SNP
- 19
- 29
- −10
- –
- Green
- 1
- 1
- –
- +1
- Independent
- 22
- 9
- +13
- +8
- Other
- –
- 2
- −2
- +3
- Thus, of 1223 seats filled in 2012, only 68 were filled by candidates who were not in the top three or four spots in the first count. Therefore, transfers changed the outcome of only about 6 percent of the spots. Single non-transferable vote would have provided the same results in a great majority of cases.
- Effective votes
- In the 2020 Irish election where members of Dáil Éireann, known as TDs (Dáil deputies), were elected by single transferable vote from 39 constituencies, each with between three and five seats, members were elected under STV with about the same number of votes and a large proportion of votes cast in each district were used to actually elect someone.
- Most elected members were elected by achieving the quota. Thus they were elected by receiving approximately the same number of votes. The few elected without quota received a number of votes close to quota as well. A large proportion of the votes were used to elect someone, with relatively few being wasted. Perhaps one full quota or less is not used to elect someone.
- In Cambridge, Massachusetts, under STV in 2021, 90 percent of voters saw their vote help to elect a candidate, more than 65 percent of voters saw their first choice candidate elected, and more than 95 percent of voters saw at least one of their top three choices elected.
- Benefits
- Advocates[who?] for STV argue it is an improvement over winner-take-all non-proportional voting systems such as plurality (FPTP), where vote splits commonly result in a majority of voters electing no one and the successful candidate having support from just a minority of the district voters. STV prevents in most cases one party taking all the seats and in its thinning out of the candidates in the field prevents the election of an extreme candidate or party if it does not have enough overall general appeal.
- History
- Carl Andræ
- Origin
- The concept of transferable voting was first proposed by Thomas Wright Hill in 1819. The system remained unused in public elections until 1855, when Carl Andræ proposed a transferable vote system for elections in Denmark, and his system was used in 1856 to elect the Rigsraad and from 1866 it was also adapted for indirect elections to the second chamber, the Landsting, until 1915.
- Thomas Hare
- Although he was not the first to propose transferable votes, the British barrister Thomas Hare is generally credited with the conception of STV, and he may have independently developed the idea in 1857. Hare's view was that STV should be a means of "making the exercise of the suffrage a step in the elevation of the individual character, whether it be found in the majority or the minority." In Hare's original system, he further proposed that electors should have the opportunity of discovering which candidate their vote had ultimately counted for, to improve their personal connection with voting. At the time of Hare's original proposal, the UK did not use the secret ballot, so not only could the voter determine the ultimate role of their vote in the election, the elected MPs would have been able to determine who had voted for them. As Hare envisaged that the whole House of Commons be elected "at large" this would have replaced geographical constituencies with what Hare called "constituencies of interest" – those people who had actually voted for each MP. In modern elections, held by secret ballot, a voter can discover how their vote was distributed by viewing detailed election results. This is particularly easy to do using Meek's method, where only the final weightings of each candidate need to be published. The elected member cannot verify who their supporters are.
- The noted political essayist John Stuart Mill was a friend of Hare's and an early proponent of STV, praising it at length in his essay Considerations on Representative Government, in which he writes: "Of all modes in which a national representation can possibly be constituted, this one affords the best security for the intellectual qualifications desirable in the representatives. At present... the only persons who can get elected are those who possess local influence, or make their way by lavish expenditure...." His contemporary, Walter Bagehot, also praised the Hare system for allowing everyone to elect an MP, even ideological minorities, but also argued that the Hare system would create more problems than it solved: "[the Hare system] is inconsistent with the extrinsic independence as well as the inherent moderation of a Parliament – two of the conditions we have seen, are essential to the bare possibility of parliamentary government."
- Advocacy of STV spread throughout the British Empire, leading it to be sometimes known as British Proportional Representation. In 1896, Andrew Inglis Clark was successful in persuading the Tasmanian House of Assembly to be the first parliament in the world elected by what became known as the Hare-Clark electoral system, named after himself and Thomas Hare. H. G. Wells was a strong advocate, calling it "Proportional Representation". The HG Wells formula for scientific voting, repeated, over many years, in his PR writings, to avoid misunderstanding, is Proportional Representation by the single transferable vote in large constituencies.
- STV in large constituencies and multiple-member districts permits an approach to the Hare-Mill-Wells ideal of mirror representation. The UK National Health Service used to elect, through the first-past-the-post system in local or regional elections, only white male general practitioners to the General Medical Council. In 1979, the UK National Health Service used STV to proportionally elect women and immigrant GPs, and specialists, to the General Medical Council.
- Main article: History and use of the single transferable vote
- Australia
- Australian Senate ballot paper used in Victoria for 2016
- Tasmania first used STV for election of members of the Tasmanian House of Assembly from 1896 to 1902. In 1909, it began to be used on a permanent basis for Assembly elections. (Instant-runoff voting was used for elections to the Tasmania Legislative Council (its upper house), with some of the members elected through STV prior to 1946.)
- In 1948, single transferable vote proportional representation on a state-by-state basis became the method for electing Senators to the Australian Senate. This change has led to the rise of a number of minor parties such as the Democratic Labor Party, Australian Democrats and Australian Greens who have taken advantage of this system to achieve parliamentary representation and the balance of power. From the 1984 election, group ticket voting was introduced to reduce a high rate of informal voting but in 2016, group tickets were abolished to avoid undue influence of preference deals amongst parties that were seen as distorting election results and a form of optional preferential voting was introduced.
- Beginning in the 1970s, Australian states began to reform their upper houses to introduce proportional representation in line with the Federal Senate. The first was the South Australian Legislative Council in 1973, which initially used a party list system (replaced with STV in 1982), followed by the single transferable vote being introduced for the New South Wales Legislative Council in 1978, the Western Australian Legislative Council in 1987 and the Victorian Legislative Council in 2003. The single transferable vote was also introduced for the elections to the Australian Capital Territory Legislative Assembly after a 1992 referendum.
- The term STV in Australia refers to the Senate electoral system, a variant of Hare-Clark characterized by the "above the line" group voting ticket, a party list option. It is used in the Australian upper house, the Senate, most state upper houses, the Tasmanian lower house and the Capital Territory assembly. There is a compulsory number of preferences for a vote for candidates (below-the-line) to be valid: for the Senate a minimum of 90% of candidates must be scored, in 2013 in New South Wales that meant writing 99 preferences on the ballot. Therefore, 95% and more of voters use the above-the-line option, making the system, in all but name, a party list system. Parties determine the order in which candidates are elected and also control transfers to other lists and this has led to anomalies: preference deals between parties, and "micro parties" which rely entirely on these deals. Additionally, independent candidates are unelectable unless they form, or join, a group above-the-line. Concerning the development of STV in Australia researchers have observed: "... we see real evidence of the extent to which Australian politicians, particularly at national levels, are prone to fiddle with the electoral system".: 86
- As a result of a parliamentary commission investigating the 2013 election, from 2016 the system has been considerably reformed (see 2016 Australian federal election), with group voting tickets (GVTs) abolished and voters no longer required to fill all boxes.
- In 2023, the Single Transferable Vote was also chosen as the electoral method in South Australia for the state's First Nation's Voice to Parliament.
- Canada
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- STV was used to elect legislators in two Canadian provinces between 1920 and 1955. The cities of Edmonton and Calgary elected their MLAs through STV from 1924 to 1956, when the Alberta provincial government changed those elections to use the first-past-the-post system. The city of Winnipeg elected its MLAs through STV from 1920 to 1955, when the Manitoba provincial government changed those elections to use first-past-the-post.
- Less well known is STV use at the municipal level in western Canada. Calgary and Winnipeg used STV for more than 50 years before city elections were changed to use the first-past-the-post system. Nineteen other municipalities, including the capital cities of the other three western provinces, also used STV For elections in about 100 elections during the 1918 to 1931 period.
- In British Columbia, Canada, a type of STV called BC-STV was recommended for provincial elections by the British Columbia Citizens' Assembly on Electoral Reform in 2004. In a 2005 provincial referendum, it received 58 percent support and achieved a simple majority in 77 of 79 electoral districts. It was rejected for falling short of the 60 percent threshold that had been set by the BC Liberal provincial government. In a second referendum, on 12 May 2009, BC-STV was defeated 61 percent to 39 percent.
- United States
- See also: Ranked-choice voting in the United States
- In the United States, the Proportional Representation League was founded in 1893 to promote STV, and their efforts resulted in its adoption by many city councils in the first half of the 20th century. More than twenty cities have used STV, including Cleveland, Cincinnati and New York City. As of January 2010, it is used to elect the city council and school committee in Cambridge, Massachusetts, the park board in Minneapolis, Minnesota, and the board of assessors in Arden, Delaware. STV has also been adopted for student government elections at several American universities, including Carnegie Mellon, MIT, Oberlin, Reed, UC Berkeley, UC Davis, Vassar, UCLA, Whitman, and UT Austin. The Fair Representation Act, introduced in Congress in June 2017, would have established STV for US House elections starting in 2022.
- List of users
- STV has seen its widest adoption in the English-speaking world.
- National legislatures
- The table below lists countries that use STV to fill a nationally elected legislative body by direct elections.
- Country
- Body
- Type of body
- Quota
- Constituencies
- District magnitude
- Governmental system
- Since
- Notes
- Australia
- Senate
- Upper house of legislature
- Droop quota
- States and territories of Australia
- 6 (for each state)
- 2 (for each territory)
- Parliamentary system
- 1948
- With the option of using a group voting ticket from 1983 until 2016
- At a full senate election triggered by a double dissolution, all 12 senators for each state are elected.
- Ireland
- Dáil Éireann
- Lower house of legislature
- Droop quota
- Constituencies
- 3–5
- Parliamentary system
- 1921
- Constituencies have a constitutionally mandated minimum magnitude of 3, and a legally mandated maximum magnitude of 5
- Malta
- House of Representatives
- Unicameral legislature
- Hagenbach-Bischoff quota
- Constituencies
- 5
- Parliamentary system
- 1921
- If elected members are from only two parties, the party with the highest first-preference vote is allocated additional members to reach majority if necessary
- Other bodies
- Country
- Body/region
- Notes
- Australia
- Australian Capital Territory
- Legislative Assembly elections (since 1992)
- Norfolk Island
- Local government elections (since 2016)
- Northern Territory
- Local government elections (since 2011)
- New South Wales
- Legislative Council elections (since 1978 – with the option of using a group voting ticket until 2003)
- Local government elections (since 2012)
- South Australia
- Legislative Council elections (since 1982 – with the option of using a group voting ticket from 1985 until 2017)
- Local government elections (since 1999)
- Local First Nations Voice elections (since 2023)
- Tasmania
- House of Assembly elections (since 1896)
- Local government elections (since 1993)
- Victoria
- Legislative Council elections (since 2003 – with the option of using a group voting ticket)
- Local government elections (since 2003)
- Western Australia
- Legislative Council elections (since 1987 – with the option of using a group voting ticket until 2021)
- Ireland
- Ireland's delegation to the European Parliament
- Since 1979
- Local government elections
- Since 1920
- Malta
- Malta's delegation to the European Parliament
- Local government elections
- New Zealand
- Local government elections
- Regional council elections: Wellington Regional Council
- Unitary authority elections: Marlborough District Council
- Territorial authority elections:
- Dunedin City Council, Kaipara District Council, Kapiti Coast District Council, New Plymouth District Council, Palmerston North City Council, Porirua City Council, Ruapehu District Council, Tauranga City Council, Wellington City Council
- Later additions – Hamilton City Council (2020)
- In 2022, this number further increased.
- District health board elections: all 20 boards (until the District Health Boards were replaced in 2021)
- United Kingdom
- Northern Ireland
- Northern Ireland Assembly elections (since 1998)
- Local government elections
- Scotland
- Local government elections (since May 2007)
- United States
- Local government elections
- City elections in Cambridge, Massachusetts (multi-member, at-large district), Eastpointe, Michigan, Palm Desert, California, Albany (NY), St. Paul (MN), St. Louis Park (MN), and Portland, Maine (multi-member, at-large district).
- At-large municipal board seats in Minneapolis, Minnesota
- Historically during the Progressive Era in 21 other cities between 1915 and 1960, including New York City for New York City Council from 1937 to 1947 (multi-winner districts)
- Indirect
- Country
- Body/region
- Notes
- Ireland
- Seanad general elections
- Upper house, since 1925
- India
- Rajya Sabha
- Vidhan Parishad (in few states)
- Nepal
- National Assembly
- Upper house elections by provinces and local assemblies since 2018
- Pakistan
- Senate
- Indirect by provincial assemblies and direct by Federally Administered Tribal Areas)
- Historic use
- Country
- Body/region
- Direct/indirect
- From
- Until
- Replaced by
- Notes
- Estonian SSR
- Supreme Soviet
- Direct
- 1990
- 1992
- Party-list proportional representation
- Canada
- Provincial legislative assemblies of Alberta and Manitoba
- Direct
- 1920s
- 1950s
- First-past-the-post voting
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