An application of coalition power analysis in group decision based on the blockability index into decision support for management in shareholders meeting

This paper aims to provide an application of an analytical method for the analysis of coalition power in group decision situations based on the blockability index on simple games, and to present that the method gives effective information for decision makers to make appropriate decisions, taking a shareholders meeting in Japan as an example. In this paper, the voting situation in the 39th Fiscal Year Shareholders Meeting of Aderans Holdings, in which the Management and the largest shareholder Steel Partners Japan (SPJ) are in a serious conflict, is mathematically modeled as a six-player simple game in the framework of the theory of cooperative games, and each coalition's power is evaluated by the blockability index. The result indicates that SPJ by itself is so powerful that the Management should get many shareholders on its side to pass its proposals. More realistic analysis is made in which possible coalitions are restricted only to feasible ones, based on each shareholder's position toward the Management. It shows that the Management must get all the shareholders except SPJ and itself on its side to have more power than SPJ. These results indicating difficulty of the Management's winning to SPJ are consistent with the reality, in which the Management's proposal was voted down.