Strategy-Proof Judgment Aggregation

25 Pages Posted: 11 Jul 2008

See all articles by Franz Dietrich

Franz Dietrich

Paris School of Economics & CNRS

Christian List

LMU Munich; London School of Economics

Date Written: August 2005

Abstract

In the theory of judgment aggregation on logically 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 Gibbard-Satterthwaite theorem. Among other escape-routes from the impossibility, we discuss weakening strategy-proofness itself. Comparing two prominent aggregation rules, 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.

JEL Classification: I21, O15

Suggested Citation

Dietrich, Franz and List, Christian, Strategy-Proof Judgment Aggregation (August 2005). LSE STICERD Research Paper No. PEPP09, Available at SSRN: https://ssrn.com/abstract=1158331

Franz Dietrich (Contact Author)

Paris School of Economics & CNRS ( email )

48 Boulevard Jourdan
Paris, 75014 75014
France

HOME PAGE: http://www.franzdietrich.net

Christian List

LMU Munich ( email )

Munich
Germany

London School of Economics ( email )

London
United Kingdom

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