投票力分析による重み付き投票集団における提携形成の評価

抄録

The present paper uses the voting power analysis, and proposes two criteria for evaluating the effectiveness of coalition formation in a weighted voting body. They are called the“ criterion of effectiveness of coalition body(El)” and the“ criterion of effectiveness of coalitional members(E2)”. Introducing the Banzhaf measure as an index of voting power we have three theoretical results: (1)The criteria are independent each other, i. e., one does not include the other and vice versa. (2)The expected frequency that a coalition satisfies El is inversely proportional to the number of members in it, but the expected frequency that it satisfies E2 is directly proportional to that. (3)Defining the well-known concepts of veto holder and dummy on the index we prove the necessary condition that a coalition satisfies the two criteria, that is all members in a coalition are not veto holders and at least two members are not dummies. Finally, by using the proposed two criteria we evaluate the effectiveness of all possible coalitions in the House of Representatives of Japan.