STAR voting: Difference between revisions

Voters cast ballots as in score voting, rating each candidate on a numerical scale. The two candidates with the highest total or average are selected, and the pairwise winner between those two is the overall winner.

== Usage ==

The concept was first proposed publicly in October 2014 by Center for Election Science co-founder Clay Shentrup.<ref>{{Cite web |url = https://groups.google.com/d/msg/electionscience/JK82EFn7nrs/Lble3V2CW4UJ |title = Google Groups |website = groups.google.com |access-date = 2017-04-05 }}</ref> The runoff step was introduced in order to correct for strategic distortion in ordinary score voting,<ref>{{Cite web |url = https://ivn.us/2016/12/08/score-runoff-voting/ |title = Score Runoff Voting: The New Voting Method that Could Save Our Democratic Process |date = 2016-12-08 |website = IVN.us |access-date = 2017-04-05 }}</ref> such as [[Bullet voting]] and tactical maximization.<ref>{{Cite news |url = http://equal.vote/strategic_srv |title = Strategic SRV? - Equal Vote Coalition |work = Equal Vote Coalition |access-date = 2017-04-05 }}</ref> Thus, STAR is intended to be a compromise between [[score voting]] and [[instant runoff voting]].<ref>{{Cite news |url = http://equal.vote |title = Equal Vote Coalition |work = Equal Vote Coalition |access-date = 2017-04-05 }}</ref> The movement to implement STAR voting was centered in [[w:Oregon|Oregon]], and in July 2018, supporters submitted over 16000 signatures for a ballot initiative in [[w:Lane County, OR|Lane County]]. This is enough to qualify this proposal to be on the ballot, if the measure is deemed well-drafted.<ref>{{Cite news |url = https://ivn.us/2018/07/09/revolutionary-new-voting-method-bolstered-16000-voters-oregon-county/ |title = Revolutionary New Voting Method Bolstered By over 16,000 Voters in Oregon County |date = 2015-07-09 |newspaper = The Independent Voter Network |access-date = 2016-7-10 }}</ref>

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.<ref>{{Cite web |url = http://rangevoting.org/RateScaleResearch.html |title = Rating Scale Research |last = |first = |date = |website = RangeVoting.org |publisher = |access-date = 2016-12-11 |quote = The evidence surveyed here currently suggests that the "best" scale for human voters should have 10 levels }}</ref> 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 higher on a greater number of ballots is the winner.

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. It fails several generalized versions of monotonicity that [[Score voting]] passes.

STAR passes the [[Majority criterion|majority criterion]], and thus is equivalent to [[Choose-one FPTP voting|choose-one FPTP voting]] whenever voters indicate all of their preferences, only in the one- or two-candidate cases (because a majority of voters will have scored their 1st choice higher than all other candidates, and with only at most two candidates in the race, the runoff must include all candidates, so majority's 1st choice will win the runoff), and passes the [[Majority criterion for rated ballots|majority criterion for rated ballots]] in the ''n''-candidate case if the majority gives no support to at least (''n'' - 2) of the candidates (because the majority's 1st choice will have over 50% [[Approval rating|approval]], while the most approval the (''n'' - 2) candidates with the fewest points can get is strictly less than 50%, due to receiving support from at most 50% - 1 of the voters. Thus, the majority's 1st choice will be one of the top two highest-scored candidates and enter the runoff, and then win).

In general, STAR voting passes a weak form of the [[mutual majority criterion]]. This is because whenever at least half of the voters give every candidate in a set of candidates the maximal score and at least all but one candidate not in the set the minimal score, and all candidates not in the set a lower score than any candidates in the set (i.e. a less than maximal score), then they guarantee that at least one of the candidates in the set at least ties to enter the runoff, or ties or wins overall (because every candidate in the set has at least 50% approval, and all but one of the candidates not in the set has at most 50% approval, with only one candidate not in the set possibly having over 50% approval. Therefore, at worst, all candidates in the set are tied with some candidates not in the set to take the second spot in the runoff; if at least one candidate in the set enters the runoff, one of the candidates in the set is guaranteed to at least tie in the runoff, since at least half of the voters scored them higher than the other candidate, unless both candidates in the runoff are candidates from the set, in which case, one of the candidates from the set is guaranteed to win). If a majority does this, they guarantee one of the candidates in the set enters the runoff and wins, rather than only tie to enter the runoff or tie or win overall (because the candidates in the set will have over 50% approval, with the most approval any of all but one of the candidates not in the set possibly getting being less than 50% approval, therefore at least one of the candidates in the set will be among the two highest-scored candidates, and then one of the candidates in the set will win the runoff because either a majority scored them higher than the other candidate, or both candidates in the runoff are candidates from the set).

A STAR voting ranking of candidates can be done by using the [[Bloc voting|Bloc STAR voting]] procedure: find the STAR winner, put them in 1st place, then remove them from the election, and repeat, putting each consecutive STAR winner in a lower rank than all previous STAR winners. Optionally, if two candidates tie in the automatic runoff during this procedure, they can both be put as tied for the same rank, and then both are removed from the election. Note that while STAR voting can never put someone ranked 3rd or worse by [[Score voting]] as 1st i.e. its winner (when run on the same ballots; this is because only the two candidates ranked highest by Score voting can enter the STAR automatic runoff and thus even be eligible to win), it can put the candidate Score ranked 1st (i.e. the Score winner) as its last place candidate using this procedure, since the Score winner may be a [[Condorcet loser]] i.e. a candidate who would lose an automatic runoff against any other candidate.

A simpler way of finding the STAR ranking is simply to put the STAR winner 1st, and then rank all of the other candidates below the STAR winner according to their Score voting ranking.

A modification to STAR that takes degree of preference more into account would be to make each voter's vote in the runoff only as strong as the highest score they gave to any candidate. In other words, a voter who gave their favorite a 3/5 (3 out of 5) would have only 3/5ths of a vote in the runoff, rather than a full vote. This modification allows voters to express less-than-full support for any candidate in both the score round and the runoff.

Given that STAR is an automatic form of Score voting + Runoff, one can also create an automatic "[[Approval voting]] + Runoff" method by allowing voters to rank or score candidates, and then indicate an [[Condorcet//Approval|approval threshold]] for a particular rank or score such that they'd approve all candidates at that same rank or score or a higher rank or score, and then use the ranks or scores to figure out which of the two most approved candidates is preferred by a majority.

Example of the STAR result being calculated from precinct-summable data (example modified from https://star.vote/txzfc3c9/):