Ranked voting

Ranked voting is any election voting system in which voters use a ranked (or preferential) ballot to rank choices in a sequence on the ordinal scale: 1st, 2nd, 3rd, etc. There are multiple ways in which the rankings can be counted to determine which candidate (or candidates) is (or are) elected (and different methods may choose different winners from the same set of ballots). The other major branch of voting systems is cardinal voting, where candidates are independently rated, rather than ranked.

This article is about voting systems that use ranked ballots, which can also include voting systems that use interval scale ballots, i.e. cardinal voting systems

Sample ballot of ranked voting using written numbers

The similar term "Ranked Choice Voting" (RCV) is used by the US organization FairVote to refer to the use of ranked ballots with specific counting methods: either instant-runoff voting for single-winner elections or single transferable vote for multi-winner elections. In some locations, the term "preferential voting" is used to refer to this combination of ballot type and counting method, while in other locations this term has various more-specialized meanings.

A ranked voting system collects more information from voters compared to the single-mark ballots currently used in most governmental elections, many of which use First-Past-The-Post and Mixed-Member Proportional voting systems.

There are many types of ranked voting, with several used in governmental elections. Instant-runoff voting is used in Australian state and federal elections, in Ireland for its presidential elections, and by some jurisdictions in the United States, United Kingdom, and New Zealand. A type and classification of ranked voting is called the single transferable vote, which is used for national elections in Ireland and Malta, the Australian Senate, for regional and local elections in Northern Ireland, for all local elections in Scotland, and for some local elections in New Zealand and the United States. Borda count is used in Slovenia and Nauru. Contingent vote and Supplementary vote are also used in a few locations. Condorcet methods are used by private organizations and minor parties, but currently are not used in governmental elections.

Arrow's impossibility theorem and Gibbard's theorem prove that all voting systems must make trade-offs between desirable properties, such as the preference between two candidates being unaffected by the popularity of a third candidate. Accordingly there is no consensus among academics or public servants as to the "best" electoral system.

Recently, an increasing number of authors, including David Farrell, Ian McAllister and Jurij Toplak, see preferentiality as one of the characteristics by which electoral systems can be evaluated. According to this view, all electoral methods are preferential, but to different degrees and may even be classified according to their preferentiality. By this logic, cardinal voting methods such as Score voting or STAR voting are also "preferential".

Notes

One criticism that can be made of ranked voting is that it creates a logical contradiction: if a voter ranks X>Y>Z, then the strength of their preference for X>Z must be stronger than their preference for X>Y or Y>Z, yet all 3 preferences are generally treated as equally strong in most ranked methods. Approval voting (and rated methods in general) can be thought of as a ranked method with constraints placed that fully resolve this contradiction: if an Approval ballot is thought of as a voter ranking one set of candidates equally 1st and above all others, then when a voter ranks an approved candidate above a disapproved candidate, they can't further indicate a preference between the disapproved candidates, thus ensuring that the strength of preference in each matchup is consistent with the strength in other matchups i.e. if they approve only X, then the strength of X>Y will be the same as X>Z, since the full preference is treated as X>Y=Z. Score voting takes this a step further by allowing voters to vary their degree of approval; in some sense, this can be seen in the ranked context by first using the KP transform and then converting the resulting Approval ballots into ranked ballots as mentioned above. This allows voters to essentially "vote against themselves" in certain matchups or otherwise split their ballot up in such a way that only a fraction of it shows a preference between certain candidates, while the rest of the ballot is treated as indifferent between those candidates i.e. a voter giving 100% support to A, 70% to B, and 10% for C is treated as 10% of an A=B=C voter, 60% of an A=B voter, and 30% of an A voter, thus allowing them to have, for example, only 60% of their ballot showing preference for B>C, rather than 100%.

Notes

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