Proximity and Linkages among Coalition Participants : A New Voting Power Measure Applied to the International Monetary Fund

Voting power methodology offers insights to understand coalition building in collective decision making. Using cooperative game theory, Banzhaf (1965) developed an index to capture the numerical importance of voters in coalition building. This voting power index is still widely used today in applications to international politics. Yet, it assumes that voters are symmetric and focuses on particular voters only. This paper proposes a new measure of voting power which account for the numerical proximity between voters by capturing how often they appear in winning coalitions together. The index is also developed to account for the relative importance of coalitions and the relative linkages among coalition participants. We present an application to the governance structure of the International Monetary Fund, with linkages being represented by bilateral trade between voters. The results are able to explain several important features of the functioning of this particular voting body, and may be useful for other applications of international politics