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The Instability of Robust Aggregation

Hild, Matthias (2001) The Instability of Robust Aggregation. Social Science Working Paper, 1113. California Institute of Technology , Pasadena, CA. (Unpublished)

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We discuss the feasibility of Levi's (1990) robust mode of aggregating individuals' evaluations of acts into a social choice function. We examine the process in which we refine decision-theoretic models and account for previously irrelevant parameters of a decision situation (cf. Savage's `small worlds'). Suppose that, for each individual, we consider a coarse-grained and a fine-grained decision-theoretic model, both of which are consistent with each other in a sense to be defined. We desire any social choice rule to be stable under refinements in the sense that the group choice based on fine-grained individual models and the group choice based on coarse-grained individual models agree for choices among coarse-grained alternatives. We find that any stable robust social choice rule must collapse back into ex ante aggregation. We also provide sufficient conditions, such as Pareto optimality, under which robust aggregation leads to an infinite series of reversals of group choice. For ex ante aggregation, we find that stability is ubiquitous and that it follows from independence of irrelevant alternatives.

Item Type:Report or Paper (Working Paper)
Additional Information:Published as Hild, M. (2004). The instability of robust aggregation. Social Choice and Welfare, 23(2), 207-227.
Group:Social Science Working Papers
Subject Keywords:ex ante aggregation, independence of irrelevant alternatives, refinements, robust aggregation, small worlds, social choice theory
Series Name:Social Science Working Paper
Issue or Number:1113
Classification Code:JEL: D63, D71
Record Number:CaltechAUTHORS:20170725-161917556
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79360
Deposited By: Jacquelyn Bussone
Deposited On:07 Aug 2017 23:17
Last Modified:03 Oct 2019 18:19

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