Only a Dictatorship is Efficient or Neutral

Social choice theory understands a voting rule as a mapping from preferences over possible outcomes to a specific choice or choices. However, actual election procedures often do not have this structure. Rather, in a typical election, although the outcome is an assembly comprising several people occupying different seats, voters cast their ballots for individual candidates, and these candidates have their votes tallied on a seat-by-seat basis. We prove two theorems: the only efficient seat-by-seat procedure is a dictatorship and the only neutral seat-by-seat procedure is a dictatorship.

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