Score voting

From Wikipedia, the free encyclopedia
  (Redirected from Range voting)
Jump to navigation Jump to search
On a score ballot, the voter scores all the candidates
Part of the Politics series
Electoral systems
A coloured voting box.svg Politics portal

Score voting or range voting[1][2] is an electoral system for single-seat elections, in which voters give each candidate a score, the scores are added (or averaged),[3][4] and the candidate with the highest total is elected. It has been described by various other names including evaluative voting,[5] utilitarian voting,[5] the point system, ratings summation, 0-99 voting, average voting, and utility voting. It is a type of cardinal voting electoral system.

Usage[edit]

Political use[edit]

A crude form of score voting[6][7] was apparently used in some elections in ancient Sparta, by measuring how loudly the crowd shouted for different candidates.[8] This has a modern-day analog of using clapometers in some television shows and the judging processes of some athletic competitions.

The Republic of Venice elected the Doge in a multi-round system, with the round that actually named the Doge being a three point score election (For, Neutral, Against).[9] This process was used continually, with only minor changes, for over 500 years, until the republic was conquered by Napoleon.

A modern governmental example is the selection process for the Secretary-General of the United Nations, which also has a three-point scale ("Encourage," "Discourage," and "No Opinion").

Score voting is used by the Green Party of Utah to elect officers, on a 0–9 scale.[10]

Non-political use[edit]

Wikimedia's Board of Trustees[11] and Wikipedia's Arbitration Committee[12] are elected using a three-point scale ("Support", "Neutral", "Oppose"). Ballots are tallied equivalently to averaged approval voting, with "Neutral" treated as abstention.

Non-governmental uses of score voting are common, such as in Likert scale customer satisfaction surveys (such as for a restaurant), automated telephone surveys (where one is asked to press or say a number to indicate their level of satisfaction or likelihood), and any mechanism that includes "giving some number of stars" as a rating (such as rating movies on IMDb, products at Amazon, apps in the iOS or Google Play stores, etc.) Score voting is common for things where there is no single winner: for instance on the Web, sites allow users to rate items such as movies (Internet Movie Database), comments, recipes, and many other things.

Sports such as gymnastics rate competitors on a numeric scale, although the fact that judges' ratings are public makes it less likely for them to engage in blatant tactical voting.

A multi-winner variant, re-weighted score voting, is used to select five nominees for the Academy Award for Best Visual Effects using a 0–10 scale.[13][14]

The traditional "highest grade point average" method of selecting a Valedictorian can be seen as a type of score election, wherein instructors "vote" on the student "candidates," with grades as their score-based votes.

Types[edit]

Score voting uses a ratings ballot; that is, each voter rates each candidate with a number within a specified score, such as 0 to 9[15] or 1 to 5. In the simplest system, all candidates must be rated. The scores for each candidate are then summed, and the candidate with the highest sum is the winner. (This is simpler for voters than cumulative voting, where they are not permitted to provide scores for more than some number of candidates.)

Some systems allow voters to explicitly abstain from rating certain candidates, as opposed to implicitly giving the lowest number of points to unrated candidates. In this case, a candidate's score would be the average rating from voters who did rate this candidate. However, some method must then be used to exclude candidates who received too few votes, to provide a meaningful average.[16][17]

In some competitions subject to judges' scores, a truncated mean is used to remove extreme scores. For example, score voting with truncated means is used in figure skating competitions to avoid the results of the third skater affecting the relative positions of two skaters who have already finished their performances (the independence of irrelevant alternatives), using truncation to mitigate biases of some judges who have ulterior motives to score some competitors too high or low.

Another method of counting ratings ballots is to find the median score of each candidate, and elect the candidate with the highest median score. This method is also referred to as Majority Judgment.[18][19] It could have the effect of reducing the incentive to exaggerate. A potential disadvantage is that multiway exact ties for winner may become common, although a method exists in Majority Judgment to break such ties.[18] In conventional score voting, these ties would be extremely rare. Another consequence of using medians is that adding an "all-zero ballot" can alter the election winner, which is arguably a disadvantage.

STAR Voting ballot with 6 generic candidate names, and 5 bubbles filled in, showing blank vote, tied vote, and scores that no candidate received
STAR Voting uses a standard Score Voting ballot. The counting method adds an extra step to yield the preference winner between the top two scoring candidates overall.

Another proposed variant is STAR voting (Score Then Automatic Runoff). Under this system, each voter may assign a score, from 0 to the maximum score, to any number of candidates. Of the two highest-scoring candidates, the winner is the one more voters assigned a higher score.[20] The concept was first proposed publicly in October 2014 by Center for Election Science co-founder Clay Shentrup.[21] The runoff step was introduced in order to correct for strategic distortion in ordinary score voting,[22] such as Bullet voting and tactical maximization.[23]

Score voting in which only two different votes may be submitted (0 and 1, for example) is equivalent to approval voting. As with approval voting, score voters must weigh the adverse impact on their favorite candidate of ranking other candidates highly.

The term "range voting" is used to describe a more theoretical system in which voters can express any real number within the range [0, 1]. While convenient for mathematical analysis, this scale is not practical for real-world elections, and is typically approximated as a score voting system with many possible grades, such as a slider in a computer interface.[24][25][26][27]

Example[edit]

Tennessee and its four major cities: Memphis in the south-west; Nashville in the centre, Chattanooga in the south, and Knoxville in the east

Imagine that Tennessee is having an election on the location of its capital. The population of Tennessee is concentrated around its four major cities, which are spread throughout the state. For this example, suppose that the entire electorate lives in these four cities and that everyone wants to live as near to the capital as possible.

The candidates for the capital are:

  • Memphis, the state's largest city, with 42% of the voters, but located far from the other cities
  • Nashville, with 26% of the voters, near the center of the state
  • Knoxville, with 17% of the voters
  • Chattanooga, with 15% of the voters

The preferences of the voters would be divided like this:

42% of voters
(close to Memphis) 		26% of voters
(close to Nashville) 		15% of voters
(close to Chattanooga) 		17% of voters
(close to Knoxville)
  1. Memphis
  2. Nashville
  3. Chattanooga
  4. Knoxville
  1. Nashville
  2. Chattanooga
  3. Knoxville
  4. Memphis
  1. Chattanooga
  2. Knoxville
  3. Nashville
  4. Memphis
  1. Knoxville
  2. Chattanooga
  3. Nashville
  4. Memphis

Suppose that 100 voters each decided to grant from 0 to 10 points to each city such that their most liked choice got 10 points, and least liked choice got 0 points, with the intermediate choices getting an amount proportional to their relative distance.

Voter from/
City Choice 		Memphis Nashville Chattanooga Knoxville Total
Memphis 420 (42 × 10) 0 (26 × 0) 0 (15 × 0) 0 (17 × 0) 420
Nashville 168 (42 × 4) 260 (26 × 10) 90 (15 × 6) 85 (17 × 5) 603
Chattanooga 84 (42 × 2) 104 (26 × 4) 150 (15 × 10) 119 (17 × 7) 457
Knoxville 0 (42 × 0) 52 (26 × 2) 90 (15 × 6) 170 (17 × 10) 312

Nashville, the capital in real life, likewise wins in the example. However, if voters from Knoxville and Chattanooga were to rate Nashville as 0 (so 2 for Memphis) and both sets of voters were to rate Chattanooga as 10, the winner would be Chattanooga over Nashville by 508 to 428 (and 484 for Memphis). This would be a better outcome for the voters in those cities than what they would get if they were to reflect their true preferences, and is considered to be an instance of tactical voting. Such tactical voting would be less effective if the ballots were counted using median scores (the principle behind Majority Judgment).

For comparison, note that traditional first-past-the-post would elect Memphis, even though most citizens consider it the worst choice, because 42% is larger than any other single city. Instant-runoff voting would elect the 2nd-worst choice (Knoxville), because the central candidates would be eliminated early. In Approval voting, with each voter selecting their top two cities, Nashville would win because of the significant boost from Memphis residents. A two-round system would have a runoff between Memphis and Nashville where Nashville would win.

Properties[edit]

Score voting allows voters to express preferences of varying strengths.

Score voting satisfies the monotonicity criterion, i.e. raising your vote's score for a candidate can never hurt their chances of winning, and lowering it can never help their chances. Also, score voting satisfies the participation criterion, i.e. casting a sincere vote can never result in a worse election winner (from your point of view) than if you had simply abstained from voting.

Score voting is independent of clones in the sense that if there is a set of candidates such that every voter gives the same rating to every candidate in this set, then the probability that the winner is in this set is independent of how many candidates are in the set.

In summary, score voting satisfies the monotonicity criterion, the participation criterion, the consistency criterion, independence of irrelevant alternatives, resolvability criterion, and reversal symmetry, provided voters do not have perfect information (see below; if they do have perfect information, it becomes a Condorcet method, which means it fails participation, consistency, and independence of irrelevant alternatives). It is immune to cloning, except for the obvious specific case in which a candidate with clones ties, instead of achieving a unique win. It does not satisfy either the Condorcet criterion (i.e., is not a Condorcet method) or the Condorcet loser criterion, although with all-strategic voters and perfect information the Condorcet winner is a Nash equilibrium.[28] It does not satisfy the later-no-harm criterion, meaning that giving a positive rating to a less preferred candidate can cause a more preferred candidate to lose.

It does not satisfy the majority criterion, but it satisfies a weakened form of it: a majority can force their choice to win, although they might not exercise that capability. To address this point, some proponents of score voting argue for the inclusion of an extra instant-runoff round in which a majority preference is established between the two top-rated candidates.[29]

As it satisfies the criteria of a deterministic voting method, with non-imposition, non-dictatorship, monotonicity, and independence of irrelevant alternatives, it may appear that it violates Arrow's impossibility theorem. The reason that score voting is not regarded as a counter-example to Arrow's theorem is that it is a cardinal voting method, while the "universality" criterion of Arrow's theorem effectively restricts that result to ordinal voting methods.[30]

Strategy[edit]

See also: Tactical voting § Score voting

In most cases, ideal score voting strategy for well-informed voters is identical to ideal approval voting strategy, and a voter would want to give their least and most favorite candidates a minimum and a maximum score, respectively. If one candidate's backers engaged in this tactic and other candidates' backers cast sincere rankings for the full range of candidates, then the tactical voters would have a significant[dubious – discuss] advantage over the rest of the electorate. When the population is large and there are two obvious and distinct front-runners, tactical voters seeking to maximize their influence on the result would give a maximum rating to their preferred candidate, and a minimum rating to the other front-runner; these voters would then give minimum and maximum scores to all[dubious – discuss] other candidates so as to maximize expected utility. If all voters voted in this manner, score voting is simply a scaled version of Plurality voting.[dubious – discuss] However, there are examples in which voting maximum and minimum scores for all candidates is not optimal.[31]

Exit poll experiments have shown that voters tend to vote more sincerely for candidates they perceive have no chance of winning.[32] Thus score voting may yield higher support for third party and independent candidates, unless those candidates become viable, than other common voting methods, creating what has been called the "nursery effect".[33]

This validity of this problem is further called into question by a 2009 paper which found that "experimental results support the concept of bias toward unselfish outcomes in large elections."[34] The authors observed what they termed ethical considerations dominating voter behavior as pivot probability decreased. This would imply that larger elections, or those perceived as having a wider margin of victory, would result in fewer tactical voters.

Tactical voters are faced with the initial tactic as to how highly to score their second choice candidate. The voter may want to retain expression of a high preference of their first choice over their second. But that does not allow the same voter to express a high preference of their second choice over any others.

Advocates point out that score voting methods (including approval voting) give no reason to ever dishonestly rank a less-preferred candidate over a more-preferred one in 3-candidate elections.[35] However, detractors respond that it provides motivation to rank a less-preferred and more-preferred candidate equally or near-equally (i.e., both 0-1 or both 98-99). This could lead to undemocratic results if different segments of the population used strategy at significantly different rates. (Note that traditional first-past-the-post voting forces all candidates except one to be ranked equally, so that all voters are compressing their preferences equally.)

Addressing these criticisms, the Equal Vote Coalition, a voting reform advocacy group, proposes a variant of score voting with an extra second round featuring the two top-rated candidates, in which the candidate with the majority of preference wins. It is claimed that the existence of a second round would discourage approval-style strategic ballots and exaggeration of ratings, making it behave like a hybrid of ranked and rated voting systems.[36][37][38]

Advocacy[edit]

Albert Heckscher is one of the earliest proponents, advocating for a form of score voting he called the "immanent method" in his 1892 dissertation, in which voters assign any number between -1 and +1 to each alternative, simulating their individual deliberation.[39][40][41]

Currently, score voting is advocated by The Center for Election Science, Center for Range Voting, Citoyens pour le Vote de Valeur, Counted and the website RangeVote.com. Guy Ottewell, who helped develop the method of approval voting, now endorses score voting.[42] Kenneth Arrow is on record as saying that "score [...] is probably the best."[43] No elected official in the United States is known to endorse score voting.

Since 2014, the Equal Vote Coalition advocates a variant method (STAR) with an extra second evaluation step to address some of the criticisms of traditional score voting.[44]

See also[edit]

Notes[edit]

  1. ^ "Center for Range Voting - front page". RangeVoting.org. Retrieved 2016-12-11. score voting (also known as "range voting").
  2. ^ "Score Voting". The Center for Election Science. 2015-05-21. Retrieved 2016-12-11.
  3. ^ "Social Choice and Beyond - Range Voting". socialchoiceandbeyond.com. Retrieved 2016-12-10. with the winner being the one with the largest point total. Or, alternatively, the average may be computed and the one with the highest average wins
  4. ^ "Score Voting". The Center for Election Science. 2015-05-21. Retrieved 2016-12-10. Simplified forms of score voting automatically give skipped candidates the lowest possible score for the ballot they were skipped. Other forms have those ballots not affect the candidate’s rating at all. Those forms not affecting the candidates rating frequently make use of quotas. Quotas demand a minimum proportion of voters rate that candidate in some way before that candidate is eligible to win.
  5. ^ a b Baujard, Antoinette; Igersheim, Herrade; Lebon, Isabelle; Gavrel, Frédéric; Laslier, Jean-François (2014-06-01). "Who's favored by evaluative voting? An experiment conducted during the 2012 French presidential election". Electoral Studies. 34: 131–145. doi:10.1016/j.electstud.2013.11.003. voting rules in which the voter freely grades each candidate on a pre-defined numerical scale. .. also called utilitarian voting
  6. ^ James S. Fishkin: The Voice of the People: Public Opinion & Democracy, Yale University Press 1995
  7. ^ "Ancient Sparta used score voting... sort of".
  8. ^ Stille, Alexander (2001-06-02). "Adding Up the Costs of Cyberdemocracy". New York Times. Retrieved 2009-10-03.
  9. ^ "Venetian Doges & Government". RangeVoting.org. Retrieved 2018-07-14.
  10. ^ "Utah Green Party Hosts Dr. Stein; Elects New Officers". Independent Political Report. 2017-06-27. Retrieved 2017-09-14. Using the following Range Voting System, the Green Party of Utah elected a new slate of officers
  11. ^ "Wikimedia Foundation elections/2017/Vote Questions - Meta". meta.wikimedia.org. Retrieved 2018-03-29.
  12. ^ "Wikipedia:Arbitration Committee Elections December 2017". Wikipedia. 2018-03-28.
  13. ^ "89TH ANNUAL ACADEMY AWARDS OF MERIT" (PDF). 2016. RULE TWENTY-TWO SPECIAL RULES FOR THE VISUAL EFFECTS AWARD. Five productions shall be selected using reweighted range voting to become the nominations for final voting for the Visual Effects award.
  14. ^ "Reweighted Range Voting - a PR voting method that feels like range voting". RangeVoting.org. Retrieved 2018-03-24.
  15. ^ "Rating Scale Research". RangeVoting.org. Retrieved 2016-12-11. The evidence surveyed here currently suggests that the "best" scale for human voters should have 10 levels
  16. ^ "Better "Soft Quorum" Rule". RangeVoting.org. Retrieved 2016-12-11.
  17. ^ "How Not To Sort By Average Rating". evanmiller.org. Retrieved 2016-12-11. Average rating works fine if you always have a ton of ratings, but suppose item 1 has 2 positive ratings and 0 negative ratings. ...
  18. ^ a b Michel Balinski and Rida Laraki (2007). "A theory of measuring, electing, and ranking — PNAS". Proceedings of the National Academy of Sciences. 104 (21): 8720–8725. doi:10.1073/pnas.0702634104. PMC 1885569. PMID 17496140. Retrieved 2009-08-03.
  19. ^ "VotingMJL.dvi" (PDF). Retrieved 2009-08-03.
  20. ^ "Equal Vote Coalition". Equal Vote Coalition. Retrieved 2017-04-05.
  21. ^ "Google Groups". groups.google.com. Retrieved 2017-04-05.
  22. ^ "Score Runoff Voting: The New Voting Method that Could Save Our Democratic Process". IVN.us. 2016-12-08. Retrieved 2017-04-05.
  23. ^ "Strategic SRV? - Equal Vote Coalition". Equal Vote Coalition. Retrieved 2017-04-05.
  24. ^ Hillinger, Claude (2005-05-01). "The Case for Utilitarian Voting". Universitätsbibliothek der Ludwig-Maximilians-Universität München. doi:10.5282/ubm/epub.653. Retrieved 2018-05-15. Specific UV rules that have been proposed are approval voting, allowing the scores 0, 1; range voting, allowing all numbers in an interval as scores; evaluative voting, allowing the scores -1, 0, 1.
  25. ^ "Should you be using a more expressive voting system?". VoteUp app. Retrieved 2018-05-15. Score Voting -- it’s just like range voting except the scores are discrete instead of spanning a continuous range.
  26. ^ "Good criteria support range voting". RangeVoting.org. Retrieved 2018-05-15. Definition 1: For us "Range voting" shall mean the following voting method. Each voter provides as her vote, a set of real number scores, each in [0,1], one for each candidate. The candidate with greatest score-sum, is elected.
  27. ^ Smith, Warren D. (December 2000). "Range Voting" (PDF). The “range voting” system is as follows. In a c-candidate election, you select a vector of c real numbers, each of absolute value ≤1, as your vote. E.g. you could vote (+1, −1, +.3, −.9, +1) in a 5-candidate election. The vote-vectors are summed to get a c-vector x and the winner is the i such that xᵢ is maximum.
  28. ^ Laslier, J.-F. (2006) "Strategic approval voting in a large electorate," IDEP Working Papers No. 405 (Marseille, France: Institut D'Economie Publique)
  29. ^ "Score Runoff Voting". Equal Vote Coalition. Retrieved 2016-12-04.
  30. ^ Arrow, Kenneth (August 1950). "A Difficulty in the Concept of Social Welfare". The Journal of Political Economy. 58 (4): 328–346. doi:10.1086/256963.
  31. ^ "Examples in which best Range Voting strategy is not "approval style" voting". The center for range voting.
  32. ^ "Honesty and Strategy in real-world voters". The center for range voting.
  33. ^ "The "Nursery Effect" (Executive summary)". The center for range voting.
  34. ^ Feddersen, Timothy; Gailmard, Sean; Sandroni, Alvaro (2009). "Moral Bias in Large Elections: Theory and Experimental Evidence". The American Political Science Review. 103 (2): 175–192. JSTOR 27798496.
  35. ^ Smith, Warren D. (2006). "Completion of Gibbard-Satterthwaite impossibility theorem; range voting and voter honesty" (PDF). Warren Smith, Temple University.
  36. ^ "Compare Approval". Equal Vote Coalition. Retrieved 2016-12-04.
  37. ^ "Equal Systems Science". Equal Vote Coalition. Retrieved 2018-07-14. a two-phase, one-election hybrid of the Rating and Ranked Choice categories
  38. ^ "Comparing Voting Systems: A Report Card". Equal Vote Coalition. Retrieved 2018-07-14. STAR Voting is the new and improved hybrid of RCV and Score Voting
  39. ^ Lagerspetz, Eerik (2014-06-01). "Albert Heckscher on collective decision-making". Public Choice. 159 (3–4): 327–339. doi:10.1007/s11127-014-0169-z. ISSN 0048-5829.
  40. ^ Eerik, Lagerspetz (2015-11-26). Social choice and democratic values. Cham. p. 109. ISBN 9783319232614. OCLC 930703262.
  41. ^ Heckscher, Albert Gottlieb (1892). Bidrag til Grundlæggelse af en Afstemningslære: om Methoderne ved Udfindelse af Stemmeflerhed i Parlamenter (in Danish).
  42. ^ Ottewell, Guy (April 2004). "The Arithmetic of Voting". Universal Workbench. self published. Retrieved January 8, 2010.
  43. ^ "Podcast 2012-10-06: Interview with Nobel Laureate Dr. Kenneth Arrow". The Center for Election Science. 2012-10-06. Retrieved 2018-07-23.
  44. ^ "About The Equal Vote Coalition". Equal Vote Coalition. Retrieved 2018-03-29.

External links[edit]

Retrieved from "https://en.wikipedia.org/w/index.php?title=Score_voting&oldid=881284206"