Vote splitting: Difference between revisions
Large update to do with how proportiona representation and ballot type interacts with vote splitting
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{{Wikipedia}}
A '''split vote''', or '''vote splitting''', occurs in an [[election]] when
== [[Single-mark ballot]] ==
The biggest issue with a single vote is that it can cause a high amount of vote splitting. It is particularly problematic in [[single member plurality]] elections. However, other systems which 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 irrelevant 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 dependant 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 effect from people trying to vote strategically must be considered.
== [[Preferential voting | Ordinal Ballot]]
The major advantage of such a system is to eliminate the standard forms of vote splitting which are present in [[Single-mark ballot]] systems. This effectively eliminates issues which give rise to the [[wasted vote]] or the [[Favorite betrayal criterion | favorite betrayal]] problems.
Unfortunately, it can be proven mathematically that ranked ballots cannot produce a communal preference without serious issues. There are no non-dictatorial rank voting systems that satisfy both [[Pareto Criterion]] and [[Independence of irrelevant alternatives]] in a way that can produce such a communal preference. This is known as [[Arrow's impossibility theorem]] and states that when voters have three or more candidates, no ranked voting electoral system can convert the ranked preferences of individuals into a community-wide (complete and transitive) ranking while also meeting [[Pareto Criterion]] and [[Independence of irrelevant alternatives]]. Both [[Pareto Criterion]] and [[Independence of irrelevant alternatives]] are well supported requirements by experts and the general public. The main reason that ranked ballots are still proposed as a solution to vote splitting is that the general public is not aware of the [[Arrow's impossibility theorem]]. It is mathematically complex and somewhat counter intuitive in many systems so is easily ignored. There is a large discrepancy between what the voter impact is perceived to be and what occurs in implementation.
== [[Cardinal voting systems | Cardinal Ballots]] ==
Cardinal voting systems do not have vote splitting. However, some [[Multi-Member System]] can still fail criteria related to [[Vote splitting]] such as [[Independence of irrelevant alternatives]] .
== Relation to [[Proportional Representation]] ==
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 lower [[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. [[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.
Another confusing point is that [[Proportional Representation]] is most clearly defined for [[Single-mark ballot]]s but [[Single-mark ballot]]s have the largest problem with vote splitting. When one wants to move to a system without vote splitting to improve [[Proportional Representation]] a problem is encountered when the it can no longer be clearly defined.
== Examples ==
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[[Category:Voting theory]]
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