Range voting

Usage

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

Modern uses of range voting can commonly be found 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.) 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.

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 range voting, is used to select the nominees for the Academy Award for Best Visual Effects.

Voting systems

Range voting uses a ratings ballot; that is, each voter rates each candidate with a number within a specified range, such as 0 to 9 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.

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 Judgment. 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. 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.

Another proposed variant, score runoff voting, uses score voting to choose the top two candidates, who are then pit against each other in an instant runoff based on the relative scores they received from each voter. The claimed advantages are a disincentive against strategic exaggeration, and a "majority winner" between the top two.

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.

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:

The preferences of the voters would be divided like this:

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.

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). Tactical voting is inevitable however, it is unlikely that only voters looking for one outcome would be voting tactically. Many Memphis voters would likely realise that they didn't have a chance and rank Nashville higher.

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 method would have a runoff between Memphis and Nashville where Nashville would win.

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 their chances of winning, and lowering it can never help their chances. Also, range 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.

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 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. 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 range voting argue for the inclusion of an extra instant-runoff round in which a majority preference is established between the two top-rated candidates.

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 range 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.

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 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 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. Exit poll experiments have shown that voters tend to vote more sincerely for candidates they perceive have no chance of winning. 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".

Range voting advocates argue that range 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. 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 range 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.

Advocacy

Range voting is advocated online by the election reform sites RangeVote.com, The Center for Election Science, and the Center for Range Voting. The Equal Vote Coalition advocates a variant method with an extra second round to address some of the criticisms of traditional range voting. Guy Ottewell, who helped develop the method of approval voting, now endorses range voting. No elected official in the United States is known to endorse range voting.