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TOPIC:
COHERENTLY EFFICIENT PREFERENCE AGGREGATION
ABSTRACT
This paper provides a new axiomatic foundation for Harsanyi's social welfare function by introducing a new normative criterion called coherent efficiency. Consider a group of individuals facing uncertainty about the set of available social alternatives, while being aware of the range of all possible alternatives and the applied collective choice function. Nature randomly chooses a set of available alternatives according to some probability distribution unknown to individuals, and then the group chooses an alternative from the set applying the collective choice function. We say that a choice function is coherently efficient if, for any probability distribution of the sets of available alternatives, the induced lottery over alternatives is efficient. The main result establishes that a choice function is coherently efficient if and only if it is represented as a maximizer of the weighted sum of individuals' utility functions, i.e., Harsanyi's social welfare function. This characterization holds for choice functions rationalized by a (possibly) incomplete social preference relation over the set of alternatives as well as a complete social preference relation over the set of lotteries.