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On coalitional manipulation for multiwinner elections: shortlisting

Bredereck, Robert; Kaczmarczyk, Andrzej; Niedermeier, Rolf

Shortlisting of candidates—selecting a group of “best” candidates—is a special case of multiwinner elections. We provide the first in-depth study of the computational complexity of strategic voting for shortlisting based on the perhaps most basic voting rule in this scenario, ℓ-Bloc (every voter approves ℓ candidates). In particular, we investigate the influence of several different group evaluation functions (e.g., egalitarian versus utilitarian) and tie-breaking mechanisms modeling pessimistic and optimistic manipulators. Among other things, we conclude that in an egalitarian setting strategic voting may indeed be computationally intractable regardless of the tie-breaking rule. Altogether, we provide a fairly comprehensive picture of the computational complexity landscape of this scenario.
Published in: Autonomous Agents and Multi-Agent Systems, 10.1007/s10458-021-09507-9, Springer Nature