Range voting: Wikis

  

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Range voting (also called ratings summation, average voting, cardinal ratings, score voting, 0–99 voting, or the score system or point system) is a voting system for one-seat elections under which voters score each candidate, the scores are added up, and the candidate with the highest score wins. A form of range voting was apparently used in some elections in Ancient Sparta by measuring how loudly the crowd shouted for different candidates.[1] Approval voting can be considered to be range voting with only 2 levels (approved (1) and disapproved (0)).

Contents

Voting system

Range voting uses a ratings ballot; that is, each voter rates each candidate with a number within a specified range, such as 0 to 99 or 1 to 5. Although in cumulative voting voters are not permitted to provide scores for more than some number of candidates, in range voting all candidates can be and should be rated. The scores for each candidate are summed, and the candidate with the highest sum is the winner. If voters are explicitly allowed to abstain from rating certain candidates, as opposed to implicitly giving the lowest number of points to unrated candidates, then a candidate's score would be the average rating from voters who did rate this candidate.

In some competitions subject to judges' scores, a truncated mean is used to remove extreme scores. For example, range 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 Judgement.[2][3] 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 Judgement to break such ties.[2] In conventional range 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.

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

Alternative use

The range voting concept has been used in non-political contexts also, 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. Range 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.

Range voting has been used informally by various amateur clubs to determine dates and venues for events like seasonal dinners. In one variant, any club member who wants to propose a date/time or restaurant writes it down on a whiteboard. All other members can each vote once for each new option; either by adding +1 to the total (in favour), casting no vote (neutral), or by subtracting one from the total (disapproval). At the end of the season, the club goes to the restaurant with the most votes, at the date and time with the most votes.

Example

Tennessee's four cities are spread throughout the state

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 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 Tennessee
  • 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 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 and/or both sets of voters were to rate Chattanooga as 10, the winner would be Chattanooga over Nashville by 508 to 428. 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.

Properties

Range voting allows voters to express preferences of varying strengths.

Range voting satisfies the monotonicity criterion, i.e. raising your vote's score for a candidate can never hurt his chances of winning. Also, in range voting, 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. Range voting passes the favorite betrayal criterion,[4] meaning that it never gives voters an incentive to rate their favorite candidate lower than a candidate they like less. Range voting advocates contend that this is a good property, because it leads to higher average voter satisfaction when voters are honest, and still gives voters the choice to strategically lower their scores for less preferred candidates if they choose.

Range 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, range voting satisfies the monotonicity criterion, the favorite betrayal criterion, the participation criterion, the consistency criterion, independence of irrelevant alternatives, resolvability criterion, and reversal symmetry. 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.[5] 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. 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.

As it satisfies the criteria of a deterministic voting system, with non-imposition, non-dictatorship, monotonicity, and independence of irrelevant alternatives, it may appear that it violates Arrow's impossibility theorem. The reason that range voting is not regarded as a counter-example to Arrow's theorem is that it is a cardinal voting system, while the "universality" criterion of Arrow's theorem effectively restricts that result to ordinal voting systems.[6]

Strategy

In most cases, ideal range voting strategy for well-informed voters is identical to ideal approval voting strategy, and a voter would want to give his 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 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 is to 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 other candidates so as to maximize expected utility.

However, there are examples in which voting maximum and minimum scores for all candidates is not optimal.[7] Exit poll experiments have shown that voters tend to vote more sincerely for candidates they perceive have no chance of winning.[8] Thus range 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".[9]

Range voting advocates argue that range voting systems (including approval voting) give no reason to ever dishonestly rank a less-preferred candidate over a more-preferred one in 3-candidate elections.[10] However, detractors respond that it provides motivation to rank a less-preferred and more-preferred candidate equally or near-equally (ie, both 0-1 or both 99-100). This could lead to undemocratic results if different segments of the population used strategy at significantly different rates.

Advocacy

Range voting is advocated online by the election reform sites RangeVote.com and the Center for Range Voting. Guy Ottewell, who helped develop the system of approval voting, now endorses range voting.[11] No elected official in the United States is known to endorse range voting.

Notes

  1. ^ "Adding Up the Costs of Cyberdemocracy". New York Times. http://query.nytimes.com/gst/fullpage.html?res=9406E7DB163FF931A35755C0A9679C8B63&sec=technology&spon=&pagewanted=2. Retrieved 10/03/2009.  
  2. ^ a b Michel Balinski and Rida Laraki. "A theory of measuring, electing, and ranking — PNAS". Pnas.org. http://www.pnas.org/content/104/21/8720.full. Retrieved 2009-08-03.  
  3. ^ "VotingMJL.dvi" (PDF). http://ceco.polytechnique.fr/fichiers/ceco/publications/pdf/2007-12-18-1691.pdf. Retrieved 2009-08-03.  
  4. ^ http://rangevoting.org/FBCsurvey.html
  5. ^ Laslier, J.-F. (2006) "Strategic approval voting in a large electorate," IDEP Working Papers No. 405 (Marseille, France: Institut D'Economie Publique)
  6. ^ Arrow, Kenneth (August 1950). "A Difficulty in the Concept of Social Welfare". The Journal of Political Economy 58 (4): 328–346.  
  7. ^ "Examples in which best Range Voting strategy is not "approval style" voting". The center for range voting. http://rangevoting.org/RVstrat1.html.  
  8. ^ "Honesty and Strategy in real-world voters". The center for range voting. http://rangevoting.org/HonStrat.html.  
  9. ^ "The "Nursery Effect" (Executive summary)". The center for range voting. http://rangevoting.org/NurserySumm.html.  
  10. ^ "Completion of Gibbard-Satterthwaite impossibility theorem; range voting and voter honesty". Warren Smith, Temple University. http://www.math.temple.edu/~wds/homepage/newgibbsat.pdf.  
  11. ^ Ottewell, Guy (April 2004). "The Arithmetic of Voting". Universal Workbench. self published. http://www.universalworkshop.com/ARVOfull.htm. Retrieved January 8, 2010.  

See also

External links








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