STAR voting

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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.

STAR voting is an electoral system for single-seat elections.[1][2][3] The name (an allusion to star ratings) stands for "Score then Automatic Runoff", referring to the fact that this system is a combination of score voting, to pick two frontrunners with the highest total scores, followed by a "virtual runoff" in which the frontrunner who is preferred on more ballots wins. It is a type of cardinal voting electoral system.

Usage[edit]

The concept was first proposed in October 2014 by Mark Frohnmayer, and was initially called score plus top two or score runoff voting (SRV).[4] The runoff step was introduced in order to reduce strategic incentives in ordinary score voting,[5] such as bullet voting and tactical maximization.[6] Thus, STAR is intended to be a hybrid between (rated) score voting and (ranked) instant runoff voting.[7][8] The movement to implement STAR voting was centered in Oregon[9][10], and in July 2018, supporters submitted over 16000 signatures for a ballot initiative in Lane County, OR, putting Measure 20-290 on the November 2018 ballot.[2][11][12][13]

Types[edit]

STAR voting uses a ratings ballot; that is, each voter rates each candidate with a number within a specified range, such as 0 to 5 stars.[14] In the simplest system, all candidates must be rated. The scores for each candidate are then summed, and the two candidates with the highest sums go to the runoff. Of these two, the one that is rated higher on a greater number of ballots is the winner.

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 5 stars to each city such that their most liked choice got 5 stars, and least liked choice got 0 stars, with the intermediate choices getting an amount proportional to their relative distance.

Voter from/
City Choice
Memphis Nashville Chattanooga Knoxville Total
Memphis 210 (42 × 5) 0 (26 × 0) 0 (15 × 0) 0 (17 × 0) 210
Nashville 84 (42 × 2) 130 (26 × 5) 45 (15 × 3) 34 (17 × 2) 293
Chattanooga 42 (42 × 1) 52 (26 × 2) 75 (15 × 5) 68 (17 × 4) 237
Knoxville 0 (42 × 0) 26 (26 × 1) 45 (15 × 3) 85 (17 × 5) 156

The top-two frontrunners are Nashville and Chattanooga. Of the two, Nashville is preferred by 68% (42+26) to 32% (15+17) of voters, so Nashville, the capital in real life, likewise wins in the example.

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. Under Score voting, Nashville would also have won, since it had the highest score in the first round. In Approval voting, with each voter selecting their top two cities, Nashville would also 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.

In this particular case, there is no way for any single city of voters to get a better outcome through tactical voting. However, Chattanooga and Knoxville voters combined could vote strategically to make Chattanooga win; while Memphis and Nashville voters could defend against that strategy and ensure Nashville still won by strategically giving Nashville a higher rating and/or Chattanooga and Knoxville lower ratings.

Properties[edit]

Unlike ranked voting systems, STAR voting allows voters to express preferences of varying strengths.

STAR 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.[15][16] It also satisfies the resolvability criterion (in both Tideman and Woodall's versions).

It does not satisfy the Condorcet criterion (i.e., is not a Condorcet method), although with all-strategic voters and perfect information, the Condorcet winner is a strong Nash equilibrium.[17] It does, however, satisfy the Condorcet loser criterion and the majority loser criterion.[18]

There are a number of other voting system criteria it does not satisfy. These include the majority criterion, since the highest-rated candidates that proceed to the runoff may not be the first preference of a majority. It does not satisfy the mutual majority criterion, although the more candidates there are in the mutual majority set, the greater the chances that at least one of them is among the two finalists in the runoff, in which case one of them will win. It does not always satisfy reversal symmetry (though it only violates it for exactly 3 candidates). It also violates independence of clones, participation, and consistency. 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.[19] It does not satisfy the later-no-help criterion, meaning that giving a positive rating to a less-preferred candidate can cause a more-preferred candidate to win.

These criteria are not considered important by STAR advocates, as some are mutually exclusive, and no voting system can ever meet all such criteria simultaneously. Advocates claim that STAR strikes a balance between such competing criteria, and performs better than other systems in voter satisfaction simulations.[19]

See also[edit]

Notes[edit]

  1. ^ "STAR voting - front page". starvoting.us. Retrieved 2018-07-10. 
  2. ^ a b "Revolutionary New Voting Method Bolstered By over 16,000 Voters in Oregon County". The Independent Voter Network. 2018-07-09. Retrieved 2018-09-18. 
  3. ^ "Equal Vote Coalition". Retrieved 2017-04-05. 
  4. ^ Shentrup, Clay (2018-08-04). "The birth of STAR Voting". Twitter. Retrieved 2018-08-06. 
  5. ^ "Score Runoff Voting: The New Voting Method that Could Save Our Democratic Process". Independent Voter Network. 2016-12-08. Retrieved 2017-04-05. 
  6. ^ "Strategic SRV?". Equal Vote Coalition. Retrieved 2017-04-05. 
  7. ^ "Equal Systems Science". Equal Vote Coalition. Retrieved 2018-07-14. a two-phase, one-election hybrid of the Rating and Ranked Choice categories 
  8. ^ "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 
  9. ^ "Lane County could break ground on electing leaders". 
  10. ^ "Residents could put STAR Voting on November ballot". 
  11. ^ "STAR Voting on Nov ballot!". STAR Voting For Lane County. Retrieved 2018-09-19. 
  12. ^ "November 6, 2018 General Election - Lane County". www.lanecounty.org. Retrieved 2018-09-19. 
  13. ^ "Military/Overseas Voters' Guide: Measure 20-290". 
  14. ^ "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 
  15. ^ "An analysis of FairVote's Look at STAR Voting". Equal Vote Coalition. Retrieved 2018-07-21. STAR is monotonic, IRV is not. 
  16. ^ D R Woodall, "Monotonicity and Single-Seat Election Rules", Voting matters, Issue 6, 1996. This article calls the monotonicity criterion in question "mono-raise", and also gives other monotonicity criteria that STAR voting fails. For instance, STAR voting violates "mono-raise-delete", defined as "A candidate X should not be harmed if X is raised on some ballots and all candidates now below X on those ballots are deleted from them". In the case of STAR, "deleted" would mean "given the lowest score"; deleting a candidate Y could change the runoff from X vs Y, which X wins, to X vs Z, which Z wins.
  17. ^ Laslier, J.-F. (2006) "Strategic approval voting in a large electorate," IDEP Working Papers No. 405 (Marseille, France: Institut D'Economie Publique)
  18. ^ Because of the limited number of scores available, when there are over 6 candidates voters who have a sincere preference are still forced to rate some candidates equal. Thus it is technically possible for a candidate to be a Condorcet and/or majority loser by sincere preferences, but not so going by ballots; and thus to win. However, this would not be true for a theoretical version of STAR where ratings are real numbers rather than whole numbers; and under any voter model where each voter is equally likely to express each successive preference, the probability of a Condorcet/majority loser winning under STAR approaches zero with even moderate numbers of voters.
  19. ^ a b "Farewell to Pass/Fail". STAR Voting. Retrieved 2018-07-21. STAR Voting actually fails both Later No Harm and The Favorite Betrayal Criterion - but hear us out! This is actually also desirable. ... We believe it is better for a system to fail two opposing criteria and in doing so mitigate the ways in which it fails both 

External links[edit]