Spoiler effect

Condorcet methods Positional voting Cardinal voting Quota-remainder methods Approval-based committees Fractional social choice Semi-proportional representation By ballot type Pathological response Strategic voting Paradoxes of majority rule Positive results In social choice theory and politics, a spoiler effect happens when a losing candidate affects the results of an election simply by participating.

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:[16]A man is deciding whether to order apple, blueberry, or cherry pie before settling on apple.

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 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.

This effect encourages groups of similar candidates to form an organization to make sure they don't step on each other's toes.

[note 1] 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.

[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] Spoiler effects rarely occur when using tournament solutions, where candidates are compared in one-on-one matchups to determine relative preference.

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] 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.

[15]: Thm.8.3 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.

[56] An unintentional spoiler is one that has a realistic chance of winning but falls short and affects the outcome of the election.

Montroll, being the majority-preferred candidate, would have won if the ballots were counted using ranked pairs (or any other Condorcet method).

[65] In Alaska's first-ever IRV election, Nick Begich was eliminated in the first round to advance Mary Peltola and Sarah Palin.