In social choice theory and politics, a spoiler effect happens when a losing candidate affects the results of an election simply by participating.[1][2] Voting rules that are not affected by spoilers are said to be spoilerproof[3][4]
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.[17]
Manipulation by politicians
Voting systems that violate independence of irrelevant alternatives are susceptible to being manipulated by strategic nomination. Such systems may produce an incentive to entry, increasing a candidate's chances of winning if similar candidates join the race, or an incentive to exit, reducing the candidate's chances of winning.
Some systems are particularly infamous for their ease of manipulation, such as the Borda count, which exhibits a particularly severe entry incentive, letting 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,"[18][19] and eventually led to its abandonment by the French Academy of Sciences.[19]
Other systems exhibit an exit incentive. The vote splitting effect in plurality voting demonstrates this method's strong exit incentive: if multiple candidates with similar views run in an election, their supporters' votes will be diluted, which may cause a unified opposition candidate to win despite having less support. This effect encourages groups of similar candidates to form an organization to make sure they don't step on each other's toes.[20]
In cases where there are many similar candidates, spoiler effects occur most often in first-preference plurality (FPP).[citation needed] For example, in the United States, vote splitting is common in primaries, where many similar candidates 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 running only one candidate. In a two-party system, party primaries effectively turn FPP into a two-round system.[21][22][23]
Vote splitting is the most common cause of spoiler effects in FPP. 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.[24][25] 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.[24][26]
Runoff systems
Plurality-runoff methods like the two-round system and RCV still experience vote-splitting in each round. This produces a kind of spoiler effect called a center squeeze. Compared to plurality without primaries, the elimination of weak candidates in earlier rounds reduces their effect on the final results; however, spoiled elections remain common compared to other systems.[25][27][28] As a result, instant-runoff voting still tends towards two-party rule through the process known as Duverger's law.[6][29] 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.[30][31][32]
Tournament (Condorcet) voting
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.[12] 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.[12][33][34]
Theoretical models suggest that somewhere between 90% and 99% of real-world elections have a Condorcet winner,[33][34] and the first Condorcet cycle in a ranked American election was found in 2021.[35] Some systems like the Schulze method and ranked pairs have stronger spoiler resistance guarantees that limit which candidates can spoil an election without a Condorcet winner.[36]: 228–229
Rated voting
Rated voting methods ask voters to assign each candidate a score on a scale (e.g. rating them from 0 to 10), instead of listing them from first to last. Highest median and score (highest mean) voting are the two most prominent examples of rated voting rules. Whenever 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. For this to hold, in some elections, some voters must use less than their full voting power despite having meaningful preferences among viable candidates.
The outcome of rated voting depends on the scale used by the voter or assumed by the mechanism.[37] If the voters use relative scales, i.e. scales that depend on what candidates are running, then the outcome can change if candidates who don't win drop out.[38] Empirical results from panel data suggest that judgments are at least in part relative.[39][40] Thus, rated methods, as used in practice, may exhibit a spoiler effect caused by the interaction between the voters and the system, even if the system itself passes IIA given an absolute scale.
A spoiler campaign in the United States is often one that cannot realistically win but can still determine the outcome by pulling support from a more competitive candidate.[41] The two major parties in the United States, the Republican Party and Democratic Party, have regularly won 98% of all state and federal seats.[42] The US presidential elections most consistently cited as having been spoiled by third-party candidates are 1844[43] and 2000.[44][45][46][43] The 2016 election is more disputed as to whether it contained spoiler candidates or not.[47][48][49] For the 2024 presidential election, Republican lawyers and operatives have fought to keep right-leaning third-parties like the Constitution Party off swing state ballots[50] while working to get Cornel West on battleground ballots.[51] Democrats have helped some right-leaning third-parties gain ballot access while challenging ballot access of left-leaning third-parties like the Green Party.[52] According to the Associated Press, the GOP effort to prop up possible spoiler candidates in 2024 appears more far-reaching than the Democratic effort.[53]Barry Burden argues that they have almost no chance of winning the 2024 election but are often motivated by particular issues.[54]
Third party candidates are always controversial because almost anyone could play spoiler.[55][56] This is especially true in close elections where the chances of a spoiler effect increase.[57]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.[42][58][59] Third-party campaigns are more likely to result in the candidate a third party voter least wants in the White House.[56] Third-party candidates prefer to focus on their platform than on their impact on the frontrunners.[56]
Notable unintentional spoilers
An unintentional spoiler is one that has a realistic chance of winning but falls short and affects the outcome of the election. Some third-party candidates express ambivalence about which major party they prefer and their possible role as spoiler[60][61] or deny the possibility.[62]
2009 Burlington mayoral election
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.[63] The results of every possible one-on-one election can be completed as follows:
Montroll – defeats all candidates below, including Kiss (4,064 to 3,476)
Kiss – defeats all candidates below, including Wright (4,313 to 4,061)
Wright – defeats all candidates below, including Smith (3,971 to 3,793)
Smith – defeats Simpson (5,570 to 721) and the write-in candidates
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.[63][64]
In the wake of the election, a poll found 54% of Alaskans, including a third of Peltola voters, supported a repeal of RCV.[68][69][70] 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.[71]
^Strategic voting can sometimes create additional spoiler-like behavior. However, this does not substantially affect the general order described here.
References
^Heckelman, Jac C.; Miller, Nicholas R. (2015-12-18). Handbook of Social Choice and Voting. Edward Elgar Publishing. ISBN9781783470730. A spoiler effect occurs when a single party or a candidate entering an election changes the outcome to favor a different candidate.
^ abcPoundstone, William. (2013). Gaming the vote : why elections aren't fair (and what we can do about it). Farrar, Straus and Giroux. pp. 168, 197, 234. ISBN9781429957649. OCLC872601019. IRV is subject to something called the "center squeeze." A popular moderate can receive relatively few first-place votes through no fault of her own but because of vote splitting from candidates to the right and left. ... Approval voting thus appears to solve the problem of vote splitting simply and elegantly. ... Range voting solves the problems of spoilers and vote splitting
^Borgers, Christoph (2010-01-01). Mathematics of Social Choice: Voting, Compensation, and Division. SIAM. ISBN9780898716955. Candidates C and D spoiled the election for B ... With them in the running, A won, whereas without them in the running, B would have won. ... Instant runoff voting ... does not do away with the spoiler problem entirely, although it ... makes it less likely
^ abcHolliday, Wesley H.; Pacuit, Eric (2023-02-11), Stable Voting, arXiv:2108.00542. "This is a kind of stability property of Condorcet winners: you cannot dislodge a Condorcet winner A by adding a new candidate B to the election if A beats B in a head-to-head majority vote. For example, although the 2000 U.S. Presidential Election in Florida did not use ranked ballots, it is plausible (see Magee 2003) that Al Gore (A) would have won without Ralph Nader (B) in the election, and Gore would have beaten Nader head-to-head. Thus, Gore should still have won with Nader included in the election."
^Morreau, Michael (2014-10-13). "Arrow's Theorem". Stanford Encyclopedia of Philosophy. Retrieved 2024-10-09. One important finding was that having cardinal utilities is not by itself enough to avoid an impossibility result. ... Intuitively speaking, to put information about preference strengths to good use it has to be possible to compare the strengths of different individuals' preferences.
^Green-Armytage, James (2014). "Strategic voting and nomination". Social Choice and Welfare. 42 (1). Springer: 111–138. doi:10.1007/s00355-013-0725-3. ISSN0176-1714. JSTOR43663746. S2CID253847024. Retrieved 2024-02-23. ... if two or more candidates with similar views run in the same plurality election, then the voters who support those views will be divided among them, giving an advantage to other candidates with opposed views. Therefore, it is helpful for groups of fairly like-minded people to form some kind of association – that is, a political party – which fields only one candidate per election, and which provides some kind of process for deciding whom this one candidate should be – that is, a primary.
^Santucci, Jack; Shugart, Matthew; Latner, Michael S. (2023-10-16). "Toward a Different Kind of Party Government". Protect Democracy. Archived from the original on 2024-07-16. Retrieved 2024-07-16. Finally, we should not discount the role of primaries. When we look at the range of countries with first-past-the-post (FPTP) elections (given no primaries), none with an assembly larger than Jamaica's (63) has a strict two-party system. These countries include the United Kingdom and Canada (where multiparty competition is in fact nationwide). Whether the U.S. should be called 'FPTP' itself is dubious, and not only because some states (e.g. Georgia) hold runoffs or use the alternative vote (e.g. Maine). Rather, the U.S. has an unusual two-round system in which the first round winnows the field. This usually is at the intraparty level, although sometimes it is without regard to party (e.g. in Alaska and California).
^Gallagher, Michael; Mitchell, Paul (2005-09-15). "The American Electoral System". The Politics of Electoral Systems. OUP Oxford. p. 192. ISBN978-0-19-153151-4. American elections become a two-round run-off system with a delay of several months between the rounds.
^Bowler, Shaun; Grofman, Bernard; Blais, André (2009), "The United States: A Case of Duvergerian Equilibrium", Duverger's Law of Plurality Voting: The Logic of Party Competition in Canada, India, the United Kingdom and the United States, New York, NY: Springer, pp. 135–146, doi:10.1007/978-0-387-09720-6_9, ISBN978-0-387-09720-6, retrieved 2024-08-31, In effect, the primary system means that the USA has a two-round runoff system of elections.
^ abSen, Amartya; Maskin, Eric (2017-06-08). "A Better Way to Choose Presidents"(PDF). New York Review of Books. ISSN0028-7504. Retrieved 2019-07-20. plurality-rule voting is seriously vulnerable to vote-splitting ... runoff voting ... as French history shows, it too is highly subject to vote-splitting. ... [Condorcet] majority rule avoids such vote-splitting debacles because it allows voters to rank the candidates and candidates are compared pairwise
^Borgers, Christoph (2010-01-01). Mathematics of Social Choice: Voting, Compensation, and Division. SIAM. ISBN9780898716955. Candidates C and D spoiled the election for B ... With them in the running, A won, whereas without them in the running, B would have won. ... Instant runoff voting ... does not do away with the spoiler problem entirely, although it ... makes it less likely
^McCune, David; McCune, Lori (2023-05-24). "The Curious Case of the 2021 Minneapolis Ward 2 City Council Election". The College Mathematics Journal: 1–5. arXiv:2111.09846. doi:10.1080/07468342.2023.2212548. ISSN0746-8342. The 2021 Minneapolis election for city council seat in Ward 2 contained three candidates, each of whom has a legitimate claim to be the winner, the first known example of an American political election without a Condorcet winner ...
^Schulze, Markus (2018-03-15). "The Schulze Method of Voting". arXiv:1804.02973 [cs.GT]. The Smith criterion and Smith-IIA (where IIA means "independence of irrelevant alternatives") say that weak alternatives should have no impact on the result of the elections ... the Schulze method, as defined in section 2.2, satisfies Smith-IIA.
^Arrow, Kenneth J. (2012). Social Choice and Individual Values. Yale University Press. pp. 10–11. ISBN978-0-300-17931-6. JSTORj.ctt1nqb90. Retrieved 2024-09-25. At best, it is contended that, for an individual, his utility function is uniquely determined up to a linear transformation ... the value of the aggregate (say a sum) are dependent on how the choice is made for each individual.
^ abGreen, Donald J. (2010). Third-party matters: politics, presidents, and third parties in American history. Santa Barbara, Calif: Praeger. pp. 153–154. ISBN978-0-313-36591-1.
^Herron, Michael C.; Lewis, Jeffrey B. (April 24, 2006). "Did Ralph Nader spoil Al Gore's Presidential bid? A ballot-level study of Green and Reform Party voters in the 2000 Presidential election". Quarterly Journal of Political Science. 2 (3). Now Publishing Inc.: 205–226. doi:10.1561/100.00005039. Pdf.
^Haberman, Maggie; Hakim, Danny; Corasaniti, Nick (2020-09-22). "How Republicans Are Trying to Use the Green Party to Their Advantage". The New York Times. ISSN0362-4331. Retrieved 2024-08-28. Four years ago, the Green Party candidate played a significant role in several crucial battleground states, drawing a vote total in three of them — Wisconsin, Michigan and Pennsylvania — that exceeded the margin between Donald J. Trump and Hillary Clinton.
^Levy, Marc (2024-08-21). "Democrats get a third-party hopeful knocked off Pennsylvania ballot, as Cornel West tries to get on". AP News. Retrieved 2024-08-28. Republicans and Democrats view third-party candidates as a threat to siphon critical support from their nominees, especially considering that Pennsylvania was decided by margins of tens of thousands of votes both in 2020 for Democrat Joe Biden and in 2016 for Trump.
^Slodysko, Brian (2024-07-16). "Kennedy and West third-party ballot drives are pushed by secretive groups and Republican donors". AP News. Retrieved 2024-08-25. there are signs across the country that groups are trying to affect the outcome by using deceptive means — and in most cases in ways that would benefit Republican Donald Trump. Their aim is to whittle away President Joe Biden's standing with the Democratic Party's base by offering left-leaning, third-party alternatives who could siphon off a few thousand protest votes in close swing state contests.
^ abcMilligan, Susan (March 22, 2024). "The Promise and the Perils of the Third-Party Candidate". US News and World Report. And despite the contenders' claims that the nation deserves an alternative to two unpopular major party choices, the reality, experts say, is that these back-of-the-pack candidates may well cement the election of the candidate they least want in the White House.
^ abStensholt, Eivind (2015-10-07). "What Happened in Burlington?". Discussion Papers: 13. There is a Condorcet ranking according to distance from the center, but Condorcet winner M, the most central candidate, was squeezed between the two others, got the smallest primary support, and was eliminated.
^Graham-Squire, Adam T.; McCune, David (2023-06-12). "An Examination of Ranked-Choice Voting in the United States, 2004–2022". Representation: 1–19. arXiv:2301.12075. doi:10.1080/00344893.2023.2221689.
^ abGraham-Squire, Adam; McCune, David (2022-09-11). "A Mathematical Analysis of the 2022 Alaska Special Election for US House". p. 2. arXiv:2209.04764v3 [econ.GN]. Since Begich wins both … he is the Condorcet winner of the election … AK election also contains a Condorcet loser: Sarah Palin. … she is also a spoiler candidate
^Clelland, Jeanne N. (2023-02-28). "Ranked Choice Voting And the Center Squeeze in the Alaska 2022 Special Election: How Might Other Voting Methods Compare?". p. 6. arXiv:2303.00108v1 [cs.CY].
