The Optimal Majority Rule on the Basis of the Voting Power Index

∼ 80% Majority Rule under the Weighted Voting System

Abstract

Since the achievements of Buchanan and Tullock (1962), indicating the optimal majority rule is to be determined at a level that minimizes the total cost of the decision-making costs and external costs, a supermajority system has been recognized as the product of compromise. However, in the weighted voting system, a divergence between the voting power and voting rights inevitably occurs. As a result, in the voting power per weight unit, inequality occurs between voters in the form of a transfer from the voters in minority groups to the voters in the majority. Though we have two ways to correct the inequality-the re-allocation of the voting rights and the adjustment of the majority requirement-bias leans toward the former study. In this paper, the Shapley-Shubik index is used to estimate the majority requirement level to balance the voting power per weight unit. The result indicates that a special majority of 80% strong is the optimal level.