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Voting power and voting blocs

Leech, Dennis and Leech, Robert (2006) Voting power and voting blocs. Public Choice, 127 (3-4). pp. 285-303. ISSN 1573-7101

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Identification Number: 10.1007/s11127-006-1914-8


We use the method of power indices to analyse voting power of members of a hypothetical legislature that has voting blocs. We assume social actors are motivated by the pursuit of constitutional power as measured by objective power indices, following Riker (Behavioural Science, 1959, “A test of the adequacy of the power index”) and Coleman (American Sociological Review, 1973, “Loss of Power”). We apply the Penrose index (the absolute Banzhaf index) to a voting body with 100 members. We show how the power indices of individual bloc members can be used to study the implications of the formation of blocs and how voting power varies as bloc size varies. We argue that the Shapley-Shubik index is inapplicable to this context and show that the Shapley-Shubik index per head – which has been used in some studies -is inappropriate. We briefly consider incentives to migrate between blocs. This technique of analysis has many real world applications to legislatures and international bodies. It can be generalised in a number of ways: our analysis is a priori, assuming formal voting and ignoring actual voting behaviour, but can be made empirical with voting data reflecting behaviour; the paper examines the consequences of two blocs but can easily be extended to more.

Item Type: Article
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Additional Information: Copyright © 2006 Springer New York LLC.The original publication is available at The authors gratefully acknowledge that work on this paper was partly supported by the Leverhulme Trust (Grant F/07-004m). LSE has developed LSE Research Online so that users may access research output of the School. Copyright and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Users may download and/or print one copy of any article(s) in LSE Research Online to facilitate their private study or for non-commercial research. You may not engage in further distribution of the material or use it for any profit-making activities or any commercial gain. You may freely distribute the URL (<>) of the LSE Research Online website.
Divisions: LSE
Subjects: J Political Science > JC Political theory
Date Deposited: 07 Aug 2006
Last Modified: 20 Jun 2021 00:37

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