Number of supportable candidates in various voting methods

From Electowiki
Jump to navigation Jump to search

Voting methods can be categorized based on how many candidates they allow you to support, and to what degree. The common Choose-one FPTP voting method (and the related Category:FPTP-based voting methods) only allows a voter to maximally support (up to) one candidate, and if they do this, they can't support any other candidates. Also, note that many voting methods allow supporting multiple candidates, but all of the support must add up to some amount. For example, Cumulative voting allows giving less than maximal support to multiple candidates, but all of the support must add up to maximally supporting one candidate i.e. you can give 50% of the maximal support to two candidates each, but not 60% each.

IRV and SNTV are in the same category. Some "support-one" voting methods can be generalized to allow maximally supporting more than one; see Equal-ranking methods in IRV for an example.

Block voting versions of "support-one" methods often allow "support up to the number of winners" candidates.

Cardinal methods and Condorcet methods allow maximally supporting unlimited numbers of candidates. For Condorcet, this is because you can maximally support a candidate in every head-to-head matchup independently of the other candidates (see Rated pairwise preference ballot for further discussion).

These are also often categorized as "zero-sum" and "non-zero-sum" (or independent) voting methods, because when you have given the maximum allowed support in "limited-support" voting methods, then you are guaranteeably not giving support to any of the candidates you didn't already support. This is argued to feed polarization and lack of voter choice/power.

Notes[edit | edit source]

One quirk of support-one methods is that it is generally possible to know which voters supported which candidates. For example, if candidate A has 10 votes and B 20 in FPTP, then it is known solely from this information that there were at least 30 voters in the election. That isn't the case with unlimited support systems i.e. if the candidates had approvals rather than votes, then there could be anywhere from 20 to 30 voters who picked one or both of them. Because of this, SNTV is Precinct-summable while Cardinal PR methods generally aren't.