Voting Power and Voting Blocs

Warwick Economic Working Paper No. 716

23 Pages Posted: 7 Feb 2005

See all articles by Dennis Leech

Dennis Leech

University of Warwick - Department of Economics

Robert Leech

University of London - Birkbeck College

Date Written: July 2004

Abstract

We investigate the method of power indices to study voting power of members of a legislature that has voting blocs. Our analysis is theoretical, intended to contribute to a theory of positive political science in which social actors are motivated by the pursuit of power as measured by objective power indices. Our starting points are the papers by Riker (Behavioural Science, 1959, "A test of the adequacy of the power index") and Coleman (American Sociological Review, 1973, "Loss of Power"). We argue against the Shapley-Shubik index and show that anyway the Shapley-Shubik index per head is inappropriate for voting blocs. We apply the Penrose index (the absolute Banzhaf index) to a hypothetical 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 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 many ways: our analysis is a priori (assuming formal voting and ignoring actual voting behaviour) but can be made empirical with voting data reflecting behaviour; it examines the consequences of two blocs but can easily be extended to more.

Keywords: Power Index, Penrose Index, Banzhaf Index, Shapley-Shubik Index, Voting Power

JEL Classification: C71, D71, D72

Suggested Citation

Leech, Dennis and Leech, Robert, Voting Power and Voting Blocs (July 2004). Warwick Economic Working Paper No. 716, Available at SSRN: https://ssrn.com/abstract=662361 or http://dx.doi.org/10.2139/ssrn.662361

Dennis Leech (Contact Author)

University of Warwick - Department of Economics ( email )

Coventry CV4 7AL
United Kingdom

Robert Leech

University of London - Birkbeck College ( email )

Malet Street
London, WC1E 7HX
United Kingdom

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