Monotonicity of Power Indices

Abstract: The paper investigates general properties of power indices, measuring the voting power in committees. Concepts of local and global monotonicity of power indices are introduced. Shapley-Shubik, Banzhaf-Coleman, and Holler-Packel indices areanalyzed and it is proved that while Shapley-Shubik index satisfies both local and global monotonicity property, Banzhaf-Coleman satisfies only local monotonicity without being globally monotonic and Holler-Packel index satisfies neither local nor global monotonicity .;