Negative responsiveness

[5] Perversity is often described by social choice theorists as an exceptionally severe kind of electoral pathology,[6] as such rules can have "backwards" responses to voters' opinions, where popularity causes defeat while unpopularity leads to a win.

Social choice theorists generally agree that negative responsiveness is an especially severe issue for a voting rule.

These include the single transferable vote and some implementations of mixed-member proportional representation, generally as a result of poorly-designed overhang rules.

[10] The frequency of negative response will depend on the electoral method, the candidates, and the distribution of outcomes.

Some empirical research do not have access to full ballot preference data, and thus make probabilistic estimates of transfer patterns.

With second preferences imputed from survey data, 1.7% of all elections appeared vulnerable to monotonicity anomalies (1.4% upward, 0.3% downward), significantly lower than simulated datasets from the same paper.

[22] A 2013 study using a two-dimensional spatial model of voting estimated at least 15% of IRV elections would be nonmonotonic in the best-case scenario (with only three equally-competitive candidates).

The researchers concluded that "three-way competitive races will exhibit unacceptably frequent monotonicity failures" and "In light of these results, those seeking to implement a fairer multi-candidate election system should be wary of adopting IRV.

[23] In Burlington's second IRV election, incumbent Bob Kiss was re-elected, despite losing in a head-to-head matchup with Democrat Andy Montroll (the Condorcet winner).

These include the single transferable vote and some implementations of mixed-member proportional representation, generally as a result of poorly-designed overhang rules.

A diagram showing who would win an IRV election for different electorates. The win region for each candidate is erratic, with random pixels dotting the image and jagged, star-shaped (convex) regions occupying much of the image. Moving the electorate to the left can cause a right-wing candidate to win, and vice versa.
A 4-candidate Yee diagram under IRV. The diagram shows who would win an IRV election if the electorate is centered at a particular point. Moving the electorate to the left can cause a right-wing candidate to win, and vice versa. Black lines show the optimal solution (achieved by Condorcet or score voting).