Range voting
From Free net encyclopedia
Range voting (also called ratings summation, or average voting, or cardinal ratings, or 0-99 voting, or the score system or point system) is a voting system used for single-seat elections in which votes are graded. (It could also be used for multi-seat elections, but this would not give proportional results.)
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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. Unlike cumulative voting there is no limit on the total ratings given, just on the rating given to each candidate. The scores for each candidate are summed, and the candidate with the highest sum is the winner. If voters are explicity 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 rating this candidate.
(Another method of counting ratings ballots is to find the median score of each candidate, and elect the candidate with the highest median score - see Median Ratings.)
Range voting in which only two different votes may be submitted (0 and 1, for example) is equivalent to approval voting.
Alternative Use
Apart from political elections it is also used on the Web - for rating movies (Internet Movie Database), comments (Kuro5hin), recipes, and many other things - and a similar scheme is used in the Olympics to award gold medals to gymnasts. Range voting is one of the voting methods endorsed by the Florida affiliate of the American Patriot Party. [1]
Example
Imagine an election for the capital of Tennessee, a state in the United States. In this vote, the candidates for the capital are Memphis, Nashville, Chattanooga, and Knoxville. The population breakdown by metro area is as follows:
- Memphis: 826,330
- Nashville: 510,784
- Chattanooga: 285,536
- Knoxville: 335,749
If the voters cast their ballot based strictly on geographic proximity, the voters' sincere preferences might be as follows:
42% of voters (close to Memphis)
|
26% of voters (close to Nashville)
|
15% of voters (close to Chattanooga)
| 17% of voters (close to Knoxville)
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Suppose that voters each decided to grant from 1 to 10 points to each city such that their most liked choice got 10 points, and least liked choice got 1 point, with the intermediate choices getting 5 points and 2 points.
| Voter from/ City Choice |
Memphis | Nashville | Chattanooga | Knoxville | Total |
|---|---|---|---|---|---|
| Memphis | 420 (42 * 10) | 26 (26 * 1) | 15 (15 * 1) | 17 (17 * 1) | 478 |
| Nashville | 210 (42 * 5) | 260 (26 * 10) | 30 (15 * 2) | 34 (17 * 2) | 534 |
| Chattanooga | 84 (42 * 2) | 130 (26 * 5) | 150 (15 * 10) | 85 (17 * 5) | 449 |
| Knoxville | 42 (42 * 1) | 52 (26 * 2) | 75 (15 * 5) | 170 (17 * 10) | 339 |
Nashville wins. But Memphis would have won if the voters from Memphis had reduced the points they gave Nashville from 5 down to 1 and all other votes had remained the same; voters from Chattanooga or Knoxville could restore Nashville to first place over Memphis if they raised the points they gave Nashville from 2 up to 10.
Properties
Range voting satisfies the monotonicity criterion, i.e. raising your vote's score for a candidate can never hurt his chances of winning, unlike in instant runoff voting (IRV).
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. This stands in contrast to IRV and Condorcet methods, in which casting a sincere vote can even cause one's first preference to lose, or one's last preference to win.
In contrast to rank ballot methods, range voting allows voters to express preferences of varying strengths.
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. The original definition of clone independence only applied to ranked voting methods, however, and some disagree that it can be extended to range voting in this way.
Range voting never gives voters an incentive to rate their favorite candidate lower than a candidate they like less. This is in contrast to IRV, Borda count, and Condorcet methods.
In summary, range voting satisfies the monotonicity criterion, the participation criterion, the consistency criterion, independence of irrelevant alternatives, reversal symmetry, and the plurality criterion. It does not satisfy the Condorcet criterion (i.e. is not a Condorcet method), the Condorcet loser criterion and the majority criterion.
Strategy
In most cases (when the population is large or not much is known about how others will vote), the optimal strategy for range voting is to vote as under approval voting, so that all candidates are given either the maximum score or the minimum score. For more detailed strategies, see approval voting.
Arrow's impossibility theorem
One of the advantages of range voting is that Arrow's impossibility theorem doesn't apply to it. Indeed it satisfies the criteria of a deterministic voting system, with non-imposition, non-dictatorship, monotonicity, and independence of irrelevant alternatives.
The reason that range voting is not treated as a counter-example to Arrow's theorem is that it is a cardinal voting system, while Arrow's theorem is restricted to the processing of ordinal preferences; two different sets of range votes may express the same individual ordinal preferences but lead to different overall rankings.
See also
- Consensus decision-making
- Decision making
- Democracy
- Hot or Not - a real world example
- Majoritarianism (Majority rule)
- Majority Choice Approval
- Minoritarianism