Impartial Selection and the Power of up to Two Choices

  • Antje Bjelde
  • Felix Fischer
  • Max Klimm
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9470)


We study mechanisms that select members of a set of agents based on nominations by other members and that are impartial in the sense that agents cannot influence their own chance of selection. Prior work has shown that deterministic mechanisms for selecting any fixed number of agents are severely limited, whereas randomization allows for the selection of a single agent that in expectation receives at least 1 / 2 of the maximum number of nominations. The bound of 1 / 2 is in fact best possible subject to impartiality. We prove here that the same bound can also be achieved deterministically by sometimes but not always selecting a second agent. We then show a separation between randomized mechanisms that make exactly two or up to two choices, and give upper and lower bounds on the performance of mechanisms allowed more than two choices.



We thank the anonymous referees for their suggestions to improve the presentation of the results.


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Authors and Affiliations

  1. 1.Institut Für MathematikTechnische Universität BerlinBerlinGermany

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