Single non-transferable vote


Single non-transferable vote or SNTV is a multi-winner electoral system in which each voter casts a single vote. Like first-past-the-post voting, SNTV uses basic plurality to allocate seats. Being semi-proportional, SNTV gives a chance for both small parties and large parties to be represented. Under SNTV, a single party seldom will take all seats in a city or district.
SNTV is a combination of multi-member districts and each voter casting just one vote. SNTV can be considered a variant of dot voting where each voter has only one point to assign. It can also be seen as a variant of limited voting where each elector has one vote, or as a simple version of Single Transferable Voting where votes are not transferred. Unlike block voting or limited voting, where voters can cast multiple votes, under SNTV each voter casts just one.
SNTV retains many of the problems of first-past-the-post voting, such as high incidence of wasted votes. As a result it is sometimes viewed skeptically by social choice theorists. However, its relative simplicity and easy vote-counting makes the system particularly popular for small elections to offices such as city councils, particularly when compared to the more-intricate single transferable vote system, and has resulted in the method becoming commonly used for ordering open party lists.

Voting

In any election, each voter casts one vote for one candidate in a multi-candidate race for multiple offices. Posts are filled by the candidates with more votes than the others. Thus, in a three-seat constituency, the three candidates receiving the largest numbers of votes would win office.
SNTV, like single transferable vote, can be used with non-partisan ballots, in election contests where there are no parties.

Example

Three seats are to be filled among five candidates: A, B, C, D and E fielded by 3 parties X, Y and Z.
VotesCandidateParty
2,718EY
1,999DZ
1,996CZ
1,804BY
819AX

E, D and C are the winning candidates. Thus, Party Z gets two seats and Party Y gets one seat. No one party took all the seats as might have been the result under first past the post or plurality block voting.
But counting the votes by party gives these vote tallies:
PartyVotesPercentSeats
Y4,522481
Z3,995432
X81990

Party Y has more votes than Party Z, but receives fewer seats because of an inefficient spread of votes across the candidates. If Party Y's two candidates had had more equal vote tallies, it would have won two seats and Party Z only one. Or if Party Z's candidates had received less equal vote tallies, Party Y would have won two seats even if its candidates were not equally popular.
If either party had risked trying to win all three seats, causing more vote splitting among supporters of Parties Y and Z, then A of Party X might have won a seat and either party Y or Z would then have taken one fewer seat.
Given candidates to be elected, Candidate A can guarantee success by receiving one more than of the votes, because +1 other candidates cannot each receive more than Candidate A
To determine the successful candidates, candidates' vote tallies are compared with the vote tallies of others, not with a theoretical threshold or quota. In the 2020 Vanuatuan general election, using SNTV, as few as 5 percent of the vote was enough to be elected in a seven-seat district, where about 13 percent is Droop quota.

SNTV Compared to Block Voting (multiple non-transferable voting) and Limited Voting

For example, 10,000 voters vote to elect three members. Cumulative voting is not used so each voter may not cast more than one vote for a single candidate.
  • Under block voting, each voter may cast 3 votes
  • Under Limited voting, each voter may cast 2 votes maximum.
  • Under the single non-transferable vote, each voter may cast 1 vote.
Party A has about 35% support among the electorate, Party B around 25% and the remaining voters primarily support independent candidates, but mostly lean towards party B if they have to choose between the two parties.
Percent of votes under block voting and Limited Voting is the percent of voters who voted for the candidate, not the percent of votes cast.
  • The three most-popular candidates according to voters' first preferences are elected, regardless of party affiliation.
  • Under the single non-transferable vote the number of seats are sometimes not proportionately allocated. Over-optimism and vote splitting is punished. But each popular party that runs one candidate is assured of success to that degree anyway. In this case, even though the most-popular party ran three and risked vote splitting, it did elect one member.
  • Single non-transferable vote described here is not a type of approval voting.
  • Under block voting, the three candidates of the most-popular party are elected if its supporters vote along party lines. In this case a party with only 35 percent support took all the seats.
  • Under limited voting, it is most likely that the party with a plurality takes two seats, and another less-popular party receives the remaining seat.
  • STV would see each party take its due share of seats if voters mark their preferences along party lines. Thus Party A and Party B would take one seat for sure, with the third seat going to Party B due to it being the choice of supporters of the Independents if it came to choice of those two main parties. The three most-popular candidates according to vote tally are elected, regardless of party affiliation, but not necessarily in accordance with first preferences.

    Non-proportionality

SNTV increases political fragmentation and representation of small parties compared to first-past-the-post voting, that is, it produces mixed representation of large and small parties where no party takes all the seats. But not having transfers, SNTV sees more votes wasted than under STV due to votes being placed on un-electable candidate or due to surpluses received by successful candidate over and above the quota used in STV elections that are not able to be transferred under SNTV. In 2007 Scottish local authority elections, only 73 out of 1222 members were not in winning position in the first round, so only 73 owed their wins to vote transfers.
Representation elected under SNTV is more proportional when political parties have accurate information about their relative levels of electoral support, and nominate candidates in accordance with their respective levels of electoral support or when all parties suffer from poor information of that sort. Knowing the share of the votes a party will take allows it to avoid vote waste due to lessening the chance of vote splitting and inefficient placement of party support. Under 'perfect' strategic voting and strategic nomination, SNTV would be equivalent to the D'Hondt method of proportional representation.
The number of wasted votes in an SNTV election is generally lower than in first past the post elections.
SNTV generally does not achieve equal seats-to-votes ratios, because it is difficult to accurately judge their strength when deciding how many candidates to field and difficult to direct party supporters as a whole to spread their votes efficiently. If they field too many, supporters' votes might be split across too many candidates. The party votes might spread their vote numbers to the point where all of a party's candidates lose to a less thinly spread opposing party. If a party fields too few candidates, they might elect all their candidates but not win seats proportional to their level of support, and the winning candidates would have more support than necessary and thus wasting votes.
The risks of poor strategic nomination are not equal for parties of various strengths. A large party would have much more to lose from the split vote effect than to gain from avoiding the wasted vote effect, and so would likely decide to err on the side of fielding fewer candidates. A small party with little representation would be more risk-tolerant and err on the side of too many candidates, hoping to gain as many seats as possible, perhaps even winning more than its proportion of the electorate if they can edge out candidates from larger parties with just a few votes. As well, a small party running just one candidate would not suffer from vote spitting, while a larger party running four or more may suffer from that.
SNTV electoral systems typically produce more proportional electoral outcomes as the size of the electoral districts increases.

Strategic voting

in a single non-transferable vote system is frequent. Casting only one vote, a rational voter wanting to maximize the number of seats captured by his party should vote for a candidate of the party that has a chance of winning, but one that will not win by too great a margin and thus take votes away from party colleagues. This creates opportunities for strategic nominations, with parties nominating candidates similar to their opponents' candidates in order to split the vote. Like all multiple-winner selections, parties find it advantageous to run a range of candidates in SNTV elections.
SNTV has been measured through the lens of such concepts as decision-theoretic analysis. Professor Gary W. Cox, an expert on SNTV, has studied this system's use in Japan. Cox has an explanation of real-world data finding the, "two systems are alike in their strategic voting equilibria." His research found that voters use the information offered in campaigns, to rationally decide who the most viable candidates are and then vote for them.
SNTV can result in complicated intra-party dynamics because in a SNTV system, a candidate runs against candidates from their own party as well as against candidates from the other party. SNTV elections are not zero-sum contests. Just because one particular candidate is elected does not mean that another specific candidate will not be. They both can be elected.
Because running on issues may lead to a situation in which a candidate becomes too popular and therefore draws votes away from other allied candidates, SNTV may encourage legislators to join factions that consist of patron-client relationships in which a powerful legislator can apportion votes to his or her supporters.
In addition, parties will do best if their supporters evenly distribute their votes among the party's candidates. Historically, in Taiwan, the Kuomintang did this by sending members a letter telling them which candidate to vote for. With the Democratic Progressive Party, vote sharing is done informally, as members of a family or small group will coordinate their votes. The New Party had a surprisingly effective system by asking party supporters to vote for the candidate whose identification number corresponded to their birthdate. This led to a system of vote allocation which had been adopted by all parties for the 2004 ROC legislative elections.