Center squeeze
A center squeeze is a kind of spoiler effect shared by rules like the two-round system, plurality-with-primaries, and ranked choice voting. In a center squeeze, the majority-preferred and socially optimal candidate is eliminated in favor of a more extreme alternative in an early round, while there are still spoilers. Systems with center squeeze are sometimes called centrifugal because they encourage political polarization.
Candidates focused on appealing to a smaller base of core supporters can "squeeze" broadly-popular candidates trapped between them out of the race, by splitting the first-preference votes needed to survive earlier rounds. This effect was first predicted by social choice theorists in the 1940s and 50s, and has since been documented in various countries using plurality-style electoral systems.
Famous examples of center squeezes include Alaska's 2022 special election as well as the 2007 French presidential election, where moderate liberal François Bayrou was eliminated by left-wing Ségolène Royal, allowing the right-wing Nicolas Sarkozy to win the second round.
Overview
Center squeezes are a kind of spoiler effect in which the majority-preferred candidate is eliminated before the final round of an election. Candidates focused on appealing to a small base of core supporters can squeeze Condorcet winners out of the race, by splitting the first-preference votes needed to survive until the final round.By Black's median-voter theorem, the candidate who appeals most to the median voter will be the majority-preferred candidate, which means they will be elected by any method compatible with majority-rule. However, in methods that strongly prioritize first preferences, these candidates are often eliminated early on because they aim for broad appeal rather than strong base support.
The "center" in "center squeeze" refers to candidates who are close to the center of public opinion, and is not limited to centrists along a traditional, one-dimensional political spectrum. A center squeeze can occur in any situation where voters prefer candidates who hold views similar to their own.
Indirect effects
Voting systems that suffer from the center-squeeze effect incentivize candidates to avoid the political center, creating political polarization in the long run. As a result, rules like RCV can lead to polarization even if center squeezes seem empirically rare, because the electoral system discourages moderates running for office in the first place.Center-squeeze has been observed in Australia, Maine, Fiji, and various US cities, all of which use ranked-choice voting, in addition to California.
Susceptibility by system
Center squeeze is a major feature of two-party systems using primaries or other multiple-round systems. In these methods, candidates must focus on appealing to their core supporters to ensure they can make it past the first round, where only first-preferences count.If voters assign scores to candidates based on ideological distance, score voting will always select the candidate closest to some central tendency of the voter distribution. As a result, while score voting does not always elect the candidate closest to the median voter, it often behaves like methods that do. Under most models of strategic voting, spoilerproof cardinal methods tend to behave like approval voting and thus converge on the Condorcet winner.
The opposite situation—a bias in favor of bland, inoffensive, or unknown candidates—is not common in any widely-used voting rules. However, it can occur for "negative" voting methods that choose candidates with the least opposition, like anti-plurality, D21 – Janeček, or Coombs' method.
Example
In Alphabet Land, voters want their name to be placed close to the start of a list. Candidate thinks names should be listed in alphabetical order, and Candidate thinks they should be in reverse-alphabetical order. Candidate thinks the order should be random.Because is preferred to both and in head-to-head match-ups, is the majority-preferred winner, and if voters' unhappiness with the result is equal to their ideological distance from the winner, will be the socially-optimal winner as well. Thus, is the "best" or "most popular" candidate under both common metrics of candidate quality in social choice.
First-preference plurality
If we use a single-round of first-preference plurality then wins, with 35.9% of voters choosing them as their favorite. However, most voters considered their least-favorite candidate, and almost two-thirds of the voters preferred to.Ranked-choice runoff (Alternative, Two-round)
tries to address vote-splitting in FPP by replacing it with a series of FPP elections, with the loser being eliminated in each round.If we use RCV instead of FPP then the first round of the election is the same as the FPP election. But then, because they have the least first preferences, is eliminated. Their votes are then reassigned to and, according to their ballot. In the second round, enough voters who preferred as their first choice took as their second choice and wins the election. RCV thus fails to have a substantial moderating impact, instead only causing a swing from one extreme to the other.
Real-world occurrences
2007 French presidential election
The 2007 French presidential election was seen as an example of a center squeeze. The second round saw Nicolas Sarkozy, a conservative, face off against Ségolène Royal, a socialist. Moderate liberal François Bayrou was eliminated in the first round, despite polls showing a majority of voters preferred Bayrou in a one-on-one match with either of his opponents.2012 Egyptian presidential election
In the 2012 Egyptian presidential election, held using the two-round system, vote-splitting among three leading moderate, non-Islamist candidates caused them all to be eliminated in the first round. This allowed the two more polarizing candidates, Mohamed Morsi and Ahmed Shafik, to advance to the runoff, despite pre-election polls suggesting the eliminated moderates would have defeated either finalist in a head-to-head contest. This led to the June 2013 Egyptian protests and 2013 Egyptian coup d'état.2022 Alaska special election
The 2022 Alaska special election seat was seen as an example of a center squeeze, where Nick Begich III was eliminated in the first round by right-wing spoiler Sarah Palin, despite a majority of voters preferring Begich to either one of his opponents. The ranked-choice runoff election involved one Democrat and two Republicans. Because the full ballot data for the race was released, social choice theorists were able to confirm that Palin spoiled the race for Begich, with Peltola winning the race as a result of several counter-intuitive behaviors that tend to characterize center-squeeze elections.The election produced a winner opposed by a majority of voters, with a majority of voters ranking Begich above Peltola and Palin, and more than half giving Peltola no support at all. The election was also notable as a no-show paradox, where a candidate is eliminated as a result of votes cast in support of their candidacy. In this case, ballots ranking Palin first and Begich second instead allowed Peltola to win.
Many social choice theorists criticized the ranked-choice runoff procedure for its pathological behavior. Along with being a center squeeze, the election was a negative voting weight event, where a voter's ballot has the opposite of its intended effect. In this race, Peltola would have lost if she had received more support from Palin voters, and won as a result of 5,200 ballots that ranked her last. However, social choice theorists were careful to note the results likely would have been the same under Alaska's previous primary system as well. This led several to recommend replacing the system with any one of several alternatives without these behaviors, such as STAR, approval, or Condorcet voting.
2009 Burlington mayoral election
The 2009 Burlington mayoral election was held in March 2009 for the city of Burlington, Vermont, and serves as an example of a four-candidate center squeeze. This was the second mayoral election since the city's 2005 change to ranked-choice runoff voting, after the 2006 mayoral election. In the 2009 election, incumbent Burlington mayor Bob Kiss won reelection as a member of the Vermont Progressive Party, defeating Kurt Wright in the final round with 48% of the vote.The election results were criticized by mathematicians and voting theorists for several pathologies associated with RCV. These included a no-show paradox, where Kiss won only as a result of 750 votes ranking Kiss in last place. Several electoral reform advocates branded the election a failure after Kiss was elected despite 54% of voters voting for Montroll over Kiss, violating the majority-rule principle. Later analyses showed the race was spoiled, with Wright pulling moderate votes away from Montroll, who would have beat Kiss in a one-on-one race.
The controversy culminated in a successful 2010 initiative that repealed RCV by a vote of 52% to 48%, a 16-point shift from the 64% who had supported the 2005 ratification. The results of every possible one-on-one election are as follows:
This leads to an overall preference ranking of:
- Montroll – defeats all candidates below, including Kiss
- Kiss – defeats all candidates below, including Wright
- Wright – defeats all candidates below, including Smith
- Smith – defeats Simpson and the write-in candidates