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Losing candidate affecting election result From Wikipedia, the free encyclopedia
In social choice theory and politics, a spoiler effect is a situation where a losing candidate's performance affects the result of an election.[1][2] A voting system that is not affected by spoilers satisfies independence of irrelevant alternatives and is called spoilerproof.[3]
Condorcet
Arrow's impossibility theorem shows that all rank-based voting systems[note 1] are vulnerable to the spoiler effect. However, the frequency and severity of spoiler effects depends substantially on the voting method. Ranked-choice voting (RCV), the two-round system (TRS), and especially plurality voting are highly sensitive to spoilers (though RCV and TRS less so in some circumstances), and all three rules are affected by center-squeeze and vote splitting.[4][5][6][7] Majority-rule (or Condorcet) methods are only rarely affected by spoilers, which are limited to rare[8][9] situations called cyclic ties.[10][11][12] Rated voting systems are not subject to Arrow's theorem, allowing many such systems to be spoilerproof.[13][14][15]
Spoiler effects can also occur in some methods of proportional representation, such as the single transferable vote (STV or RCV-PR) and the largest remainders method of party-list representation, where it is called a new party paradox. A new party entering an election causes some seats to shift from one unrelated party to another, even if the new party wins no seats.[16] This kind of spoiler effect is avoided by divisor methods and proportional approval.[16]: Thm.8.3
In decision theory, independence of irrelevant alternatives is a fundamental principle of rational choice which says that a decision between two outcomes, A or B, should not depend on the quality of a third, unrelated outcome C. A famous joke by Sidney Morgenbesser illustrates this principle:[17]
A man is deciding whether to order apple, blueberry, or cherry pie before settling on apple. The waitress informs him that the cherry pie is very good and a favorite of most customers. The man replies "in that case, I'll have the blueberry."
Politicians and social choice theorists have long argued for the unfairness of spoiler effects. The mathematician and political economist Nicolas de Condorcet was the first to study the spoiler effect, in the 1780s.[18]
Voting systems that violate independence of irrelevant alternatives are susceptible to being manipulated by strategic nomination. Some systems are particularly infamous for their ease of manipulation, such as the Borda count, which lets any party "clone their way to victory" by running a large number of candidates. This famously forced de Borda to concede that "my system is meant only for honest men,"[19][20] and eventually led to its abandonment by the French Academy of Sciences.[20]
Vote-splitting systems like choose-one and ranked-choice voting have the opposite problem: because running many similar candidates at once makes it difficult for them to win the election, these systems tend to concentrate power in the hands of parties and political machines. Under these rules, parties can help their candidates win by clearing the field of potential competitors.[21] In the United States, this leads plurality voting systems to behave like a de facto two-round system, where the top-two candidates are nominated by party primaries.[22][23][24]
In some situations, a spoiler can extract concessions from other candidates by threatening to remain in the race unless they are bought off, typically with a promise of a high-ranking political position.[citation needed]
Different electoral systems have different levels of vulnerability to spoilers. In general, spoilers are common with plurality voting, somewhat common in plurality-runoff methods, rare with majoritarian methods, and mathematically impossible with most rated voting methods.[note 2]
In cases where there are many similar candidates, spoiler effects occur most often in plurality voting.[25][better source needed] In the United States, vote splitting is common in primaries, where many similar candidates can run against each other. The purpose of a primary election is to eliminate vote splitting among candidates from the same party in the general election by agreeing to run a single individual. In a two-party system, party primaries effectively turn plurality voting into a two-round system.[22][23][24]
Vote splitting is the most common cause of spoiler effects in the plurality vote and two-round runoff systems.[26] In these systems, the presence of many ideologically similar candidates causes their vote total to be split between them, placing these candidates at a disadvantage.[27] This is most visible in elections where a minor candidate draws votes away from a major candidate with similar politics, thereby causing a strong opponent of both to win.[27][28]
Plurality-runoff methods like the two-round system and RCV can still experience spoilers in each round by a process called center squeeze. Compared to plurality without primaries, the elimination of weak candidates in earlier rounds reduces their effect on the final results. Regardless, spoiled elections remain relatively common when compared to other systems.[15][29][30] As a result, instant-runoff voting still tends towards two-party rule through the process known as Duverger's law.[14][31] A notable example of this can be seen in Alaska's 2024 race, where party elites pressured candidate Nancy Dahlstrom into dropping out to avoid a repeat of the spoiled 2022 election.[32][33][34]
Spoiler effects rarely occur when using tournament solutions, where candidates are compared in one-on-one matchups to determine relative preference. For each pair of candidates, there is a count for how many voters prefer the first candidate in the pair to the second candidate The resulting table of pairwise counts eliminates the step-by-step redistribution of votes, which is usually the cause for spoilers in other methods.[35] This pairwise comparison means that spoilers can only occur when there is a Condorcet cycle, where there is no single candidate preferred to all others.[36][37][35] In practice, somewhere between 90% and 99% of real-world elections have a Condorcet winner.[36][37]
Rated voting methods ask voters to assign each candidate a score on a scale (usually from 0 to 10), instead of listing them from first to last. Approval voting and score voting are prominent examples. Because voters rate candidates independently, the rating given to one candidate does not affect the ratings given to the other candidates. Any new candidate cannot change the winner of the race without becoming the winner themselves, which would disqualify them from the definition of a spoiler.
While true spoilers are not possible under rated systems, voters who behave strategically in response to a new candidate can create pseudo-spoiler effects, which are distinct from "true" spoilers in that they are caused by voter behavior, rather than the voting system itself. Voters may decide to pull support from one candidate upon the introduction of another, even though the voting system does not require them to do so. Should this behavior change the winner of a race, the new candidate could be considered a spoiler in the casual sense.
The two major parties in the United States, the Republican Party and Democratic Party, have regularly won 98% of all state and federal seats.[38] The US presidential elections most consistently cited as having been spoiled by third-party candidates are 1844[39] and 2000.[40][41][42][39] The 2016 election is more disputed as to whether it contained spoiler candidates or not.[43][44][45] For the 2024 presidential election, Republican lawyers and operatives have fought to keep right-leaning third-parties like the Constitution Party off of swing state ballots[46] while working to get Cornel West on battleground ballots.[47] Democrats have helped some right-leaning third-parties gain ballot access while challenging ballot access of left-leaning third-parties like the Green Party.[48] According to the Associated Press, the GOP effort to prop up possible spoiler candidates in 2024 appears more far-reaching than the Democratic effort.[49]
Third party candidates are always controversial because almost anyone could play spoiler.[50][51] This is especially true in close elections where the chances of a spoiler effect increase.[52] Strategic voting, especially prevalent during high stakes elections with high political polarization, often leads to a third-party that underperforms its poll numbers with voters wanting to make sure their least favorite candidate is not in power.[53][54][38] Third-party campaigns are more likely to result in the candidate a third party voter least wants in the White House.[51] Third-party candidates prefer to focus on their platform than on their impact on the frontrunners.[51]
In Burlington, Vermont's second IRV election, spoiler Kurt Wright knocked out Democrat Andy Montroll in the second round, leading to the election of Bob Kiss, despite the election results showing most voters preferred Montroll to Kiss.[55] The results of every possible one-on-one election can be completed as follows:
Andy Montroll (D) | 6262 (Montroll) –
591 (Simpson) |
4570 (Montroll) –
2997 (Smith) |
4597 (Montroll) –
3664 (Wright) |
4064 (Montroll) –
3476 (Kiss) |
4/4 Wins | |
---|---|---|---|---|---|---|
Bob Kiss (P) | 5514 (Kiss) –
844 (Simpson) |
3944 (Kiss) –
3576 (Smith) |
4313 (Kiss) –
4061 (Wright) |
3/4 Wins | RCV winner | |
Kurt Wright (R) | 5270 (Wright) –
1310 (Simpson) |
3971 (Wright) –
3793 (Smith) |
2/4 Wins | Spoiler for Montroll | ||
Dan Smith (I) | 5570 (Smith) –
721 (Simpson) |
1/4 Wins | ||||
James Simpson (G) | 0/4 Wins |
This leads to an overall preference ranking of:
Montroll was therefore preferred over Kiss by 54% of voters, over Wright by 56%, and over Smith by 60%. Had Wright not run, Montroll would have won instead of Kiss.[56][57]
Because all ballots were fully released, it is possible to reconstruct the winners under other voting methods. While Wright would have won under plurality, Kiss won under IRV, and would have won under a two-round vote or a traditional nonpartisan blanket primary. Montroll, being the majority-preferred candidate, would have won if the ballots were counted using ranked pairs (or any other Condorcet method).[58]
In Alaska's first-ever IRV election, Nick Begich was defeated in the first round by spoiler candidate Sarah Palin. The pairwise comparison—derived from the ballot data—shows that Begich was the Condorcet winner while Palin was both the Condorcet loser and a spoiler:[59][60][61][62][63]
In the wake of the election, a poll found 54% of Alaskans, including a third of Peltola voters, supported a repeal of RCV.[64][65][66][67] Observers noted such pathologies would have occurred under Alaska's previous primary system as well, leading several to suggest Alaska adopt any one of several alternatives without this behavior.[68][69][70]
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