Inequality in voting power

This paper deals with the assessment of inequality in the distribution of voting power. Voting power is evaluated through a general concept of power measurement based on both the voting rule and the probability distribution over vote configurations. This general concept includes as particular cases the most usual power indices and other extensions of this traditional concept. Thus no particular power index is privileged in our approach. An inequality index over the class of all power profiles with a given number of voters generated by this general measure is then singled out by requiring reasonable properties. In order to compare profiles with different numbers of voters, two alternative principles are considered, which extend the said index consistently in two ways.Previous versions of this work were circulated under different titles. We gratefully acknowledge financial support from the Spanish Ministerio de Ciencia y Tecnología under the Ramón y Cajal programme and under projects PB96-0247 and BEC2000-0875; from the European Commission under the Training and Mobility of Researchers programme (contract FMRX - CT966-0055); and from the Instituto Valenciano de Investigaciones Económicas. We also thank two anonymous referees for their comments.2 October 2001