Vote splitting: Difference between revisions

{{Wikipedia}}

 

 

The first kind of vote splitting is a consequence of the [[ballot type]]. This means more expressive ballots have less or no vote splitting, if paired with a method that safeguards against the second type of vote splitting..

The second type of vote splitting is normally defined by either unwanted consequences or [[strategic voting]] but is hard to define rigorously. There are a number of criteria related to vote-splitting which are more rigorous.

 

 

The biggest issue with a single-mark ballot is that it can cause a high amount of vote splitting. It is particularly problematic in [[single member plurality]] elections. However, other systems that still use a single-mark ballot such as [[Runoff voting]] still have vote splitting.

A standard example of vote-splitting is when two candidates are similar, so they each get half the votes they would if the other were not running. This is a good example of failing the [[Independence of clone alternatives]] criteria. Another issue is that the voter's preferred candidate may be highly unpopular in the constituency. This means that using their only vote on that candidate has no influence on the result and could be better served on a second or third choice. This is a problem of voter impact which can be thought of how clearly a voter's true choice is translated into the election of a candidate. This is often referred to as the ''[[Wasted vote]] problem'' if they still vote for their favorite or the [[Favorite betrayal criterion|favorite betrayal]] problem if they vote for another candidate. This system rewards voters for not voting for whom they really want and as such promotes [[strategic voting]]. Furthermore, it implies that the voter's choice will be heavily dependent on their estimates of how others will vote, not on their preference. The use of fake polls or deceptive reporting can have large effects on election outcomes where strategic voting is emphasized. With all systems of voting, the second-order effects of people trying to vote strategically must be considered.

 

 

The major advantage of ranked voting is to eliminate the standard forms of vote splitting which are present in [[Single-mark ballot]] systems. This can largely eliminate issues that give rise to the [[wasted vote]], though some ranked methods still fail [[independence of clones]] and most ranked methods fail the [[favorite betrayal criterion]].

Unfortunately, it can be proven mathematically that no non-random ranked ballot method can be entirely free of [[spoiler effect|spoilers]] due to [[Arrow's impossibility theorem]]. In particular, [[independence of irrelevant alternatives]] is incompatible with [[majority rule]]. Ranked ballots are still proposed as a solution to vote splitting for two reasons. First, the types of election where spoilers exist are greatly reduced; and second, for ''any'' deterministic method to be entirely free of spoilers requires some assumptions that are often considered unrealistic - see below.

 

 

Some cardinal voting systems pass [[independence of irrelevant alternatives]], meaning that the removal of a candidate who didn't win will have no effect on who won. For instance, both [[range voting]] and [[Majority Judgement]] do so.

For Majority Judgement in particular, Michel Balinski and Rida Laraki argue that the categories have common definitions, which implies that the voters' evaluation of the candidates will be independent of who is running, and hence that its [[IIA]] compliance eliminates the spoiler effect.

 

 

Vote splitting is often conflated with [[Proportional Representation]] but they are completely distinct concepts. Vote splitting is related to strategic or expression issues at the time of filling out a ballot by a voter. [[Proportional Representation]] is a measure of the outcome of an election. The relationship is that vote splitting is a major cause of reduced [[Proportional Representation]]. Systems designed to achieve high [[Proportional Representation]] but that still use [[single-mark ballot]]s often do not reduce the amount of vote splitting but instead mask its effects at the partisan level. A [[Mixed Member Proportional|mixed electoral system]], for example, still has a [[single member plurality]] component with all the vote splitting issues of a full [[single member plurality]] system.