Evaluation of Influence of Governing and Opposition Coalitions in the National Diet of Japan Using Coalition Power Index

Abstract

This paper aims to provide an evaluation of coalitions of governing and opposition parties in the House of Representatives and the House of Councillors in the National Diet of Japan, using coalition power index, which is a framework for evaluation of coalition influence in group decision. In this paper, voting situations in both Houses are mathematically modeled as simple games based on seat distribution in the respective Houses. Then, influences of feasible governing and opposition coalitions are calculated based on a coalition power index. It is shown that the calculation result gives a numerical explanation to the political situation at that time.