Strategy-proof judgment aggregation

Franz Dietrich and Christian List
Authors registered in the RePEc Author Service: John List ()

Public Economics from EconWPA

Abstract: In the theory of judgment aggregation on connected propositions, an important question remains open: Which aggregation rules are manipulable and which are strategy-proof? We define manipulability and strategy- proofness in judgment aggregation, characterize all strategy-proof aggregation rules, and prove an impossibility theorem similar to the classic Gibbard-Satterthwaite theorem. Among other ways to avoid the impossibility, we discuss weakening strategy-proofness itself. Comparing two prominent aggregation rules in the literature, we show that "conclusion-based voting" is strategy-proof, but generates incomplete judgments, while "premise-based voting" is only strategy-proof for "reason-oriented" individuals. Surprisingly, for "outcome-oriented" individuals, the two rules are strategically equivalent, generating identical judgments in equilibrium. Our results introduce game-theoretic considerations into judgment aggregation and have implications for debates on deliberative democracy.

Keywords: judgment aggregation; logic; strategic voting; strategy-proofness; characterization theorem; impossibility theorem; Gibbard-Satterthwaite theorem; doctrinal paradox; discursive dilemma; premise-based procedure; conclusion-based procedure (search for similar items in EconPapers)
JEL-codes: D70 D71 (search for similar items in EconPapers)
Date: 2004-04-18, Revised 2005-10-31
Note: Type of Document - pdf; pages: 31. pdf, prepared with latex
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Working Paper: Strategy-proof judgment aggregation (2005)
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Persistent link: http://EconPapers.repec.org/RePEc:wpa:wuwppe:0404007

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