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An Experimental Study of Jury Decision Rules

Guarnaschelli, Serena and McKelvey, Richard D. and Palfrey, Thomas R. (2000) An Experimental Study of Jury Decision Rules. Social Science Working Paper, 1034. California Institute of Technology , Pasadena, CA. (Unpublished)

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We present experimental results on individual decisions in juries. We consider the effect of three treatment variables: the size of the jury (three or six), the number of votes needed for conviction (majority or unanimity), and jury deliberation. We find evidence of strategic voting under the unanimity rule, where the form of strategic behavior involves a bias to vote guilty to compensate for the unanimity requirement. A large fraction of jurors vote to convict even when their private information indicates the defendant is more likely to be innocent than guilty. This is roughly consistent with the game theoretic predictions of Feddersen and Pesendorfer (FP) [1998]. While individual behavior is explained well by the game theoretic model, at the level of the jury decision, there are numerous discrepancies. In particular, contrary to the FP prediction, we find that in our experiments juries convict fewer innocent defendants under unanimity rule than under majority rule. We are able to simultaneously account for the individual and group data by using Quantal Response Equilibrium to model the error.

Item Type:Report or Paper (Working Paper)
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Palfrey, Thomas R.0000-0003-0769-8109
Additional Information:Revised version. Original version dated to October 1997. Support of the National Science Foundation (Grant #SBR-9617854) is gratefully acknowledged. We thank Tara Butterfield for research assistance, John Patty for help in running the experiments, and Tim Reed and Charles Smith for writing the computer program for the experiments. We also thank Tim Feddersen, Susanne Lohmann, Krishna Ladha, the audiences at several academic conferences and seminars, and three referees for their comments. Published as Guarnaschelli, S., McKelvey, R.D., & Palfrey, T.R. (2000). An experimental study of jury decision rules. American Political Science Review, 94(2), 407-423.
Group:Social Science Working Papers
Funding AgencyGrant Number
Subject Keywords:Voting, Straw, Polls, Juries, Nash equilibrium, Legal innocence, Guilt, Game theory, Majority rule, Jurors
Series Name:Social Science Working Paper
Issue or Number:1034
Record Number:CaltechAUTHORS:20170811-153843207
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:80321
Deposited By: Jacquelyn Bussone
Deposited On:11 Aug 2017 23:30
Last Modified:22 Nov 2019 09:58

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