In social choice theory with ordinal preferences, a voting method satisfies the axiom of positive involvement if adding to a preference profile a voter who ranks an alternative uniquely first cannot cause that alternative to go from winning to losing. In this note, we prove a new impossibility theorem concerning this axiom: there is no ordinal voting method satisfying positive involvement that also satisfies the Condorcet winner and loser criteria, resolvability, and a common invariance property for Condorcet methods, namely that the choice of winners depends only on the ordering of majority margins by size.
View on arXiv@article{holliday2025_2401.05657,
title={ An impossibility theorem concerning positive involvement in voting },
author={ Wesley H. Holliday },
journal={arXiv preprint arXiv:2401.05657},
year={ 2025 }
}