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Dummy Players and the Quota in Weighted Voting Games: Some Further Results

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Evaluating Voting Systems with Probability Models

Part of the book series: Studies in Choice and Welfare ((WELFARE))

Abstract

This chapter is a companion paper of Barthélémy et al. (2019) which studies the role of the quota on the occurrence of “dummy” players in small weighted voting games (i.e., in voting games with 3, 4 or 5 players). We here extend the results obtained in this paper by considering voting games with a larger number of players (up to 15). It is shown that the probability of having a player without voting power is very sensitive to the choice of the quota and the quota values that minimize this probability are derived.

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Notes

  1. 1.

    In the particular case where \(q=q_{maj}\), not only player 2 but also player 3 cannot be a dummy; see Proposition 1 in Barthélémy et al. (2013). In this case, the maximum number of dummy players is \(n-3\).

  2. 2.

    For a clear and simple presentation, see Straffin (1994).

  3. 3.

    This is an arbitrary choice. Any number of players, reasonably large, can be studied.

  4. 4.

    See Straffin (1994) for a presentation of this power index.

  5. 5.

    Obviously, other values of w or Q lead to the same kind of curves.

  6. 6.

    Note that \(Q=0.5\) and \(Q=0.6\) correspond to the same quota \(q=6\).

  7. 7.

    Note however that for high values of Q, the convergence is not clear and more players are needed in order to recover Penrose’s law.

  8. 8.

    The results we have obtained for smaller values of w are available from the authors upon request.

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Acknowledgements

Financial support from the ANR SOLITER is gratefully acknowledged. This research has been also developed within the center of excellence MME-DII (ANR-11-LBX-0023-01). Warm thanks are due to Dominique Lepelley for his valuable help.

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Correspondence to Fabrice Barthélémy .

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Barthélémy, F., Martin, M. (2021). Dummy Players and the Quota in Weighted Voting Games: Some Further Results. In: Diss, M., Merlin, V. (eds) Evaluating Voting Systems with Probability Models. Studies in Choice and Welfare. Springer, Cham. https://doi.org/10.1007/978-3-030-48598-6_13

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