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A Model of Jury Decisions Where All Jurors Have the Same Evidence

Listed author(s):
  • Franz Dietrich

    (Group on Philosophy, Probability and Modelling, University of Konstanz, Germany)

  • Christian List


    (Nuffield College, University of Oxford, Oxford, UK)

In the classical Condorcet jury model, different jurors' votes are independent random variables, where each juror has the same probability p>1/2 of voting for the correct alternative. The probability that the correct alternative will win under majority voting converges to 1 as the number of jurors increases. Hence the probability of an incorrect majority vote can be made arbitrarily small, a result that may seem unrealistic. A more realistic model is obtained by relaxing the assumption of independence and relating the vote of every juror to the same "body of evidence". In terms of Bayesian trees, the votes are direct descendants not of the true state of the world ('guilty' or 'not guilty'), but of the "body of evidence", which in turn is a direct descendant of the true state of the world. This permits the possibility of a misleading body of evidence. Our main theorem shows that the probability that the correct alternative will win under majority voting converges to the probability that the body of evidence is not misleading, which may be strictly less than 1.

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Paper provided by Economics Group, Nuffield College, University of Oxford in its series Economics Papers with number 2002-W23.

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Length: 12 pages
Date of creation: 24 Sep 2002
Handle: RePEc:nuf:econwp:0223
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  1. Daniel Berend & Jacob Paroush, 1998. "When is Condorcet's Jury Theorem valid?," Social Choice and Welfare, Springer;The Society for Social Choice and Welfare, vol. 15(4), pages 481-488.
  2. repec:cup:apsrev:v:82:y:1988:i:04:p:1231-1244_19 is not listed on IDEAS
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