Center squeeze

The center squeeze effect refers to a class of voting scenarios which are troublesome for many voting systems. In such a scenario, the strongest three candidates can be arranged on a spectrum such as "left", "center", and "right"; and of the three, the "center" candidate is the Condorcet winner but the honest Plurality loser (that is, the one with the fewest voters strictly preferring them over the other two). Most consider that if the centrist is not too far behind in honest plurality, they should be the winner, as otherwise the voting system is encouraging strategy (typically, a favorite betrayal) from one of the other two groups.

The effect is not limited to 3 candidates: The more candidates there are crowding the center, the less likely they are to win.

Example

For example, on a 2-dimensional political compass with 3 candidates, candidate B is the Condorcet winner and utilitarian winner, but is squeezed out by A and C on either side:

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Either way, the winner is not as good a representatives of the electorate as candidate B.

Prevalence

Voting systems which have serious problems with center squeeze include FPTP, IRV and two-round runoff voting.

Systems which can do either well or poorly in a center squeeze situation include most graded Bucklin systems and score voting.

Systems which generally do well with center squeeze include Condorcet systems (although in some cases, a center squeeze scenario could become an opportunity for one of the wings to use burial strategy and create an artificial Condorcet cycle).