A priori power measures and the institutions of the European Union

Abstract. The a priori voting powers of member countries in the council of ministers of the European Union have been discussed in the literature mainly from the view–point of Banzhaf and Shapley–Shubik indices. This paper discusses — in the light of these and other more recent (Colomer's, Holler's as well as Deegan and Packel's) power indices — the interaction of the council ministers and the European Parliament (EP) under the assumption that the consent of both bodies is needed to carry a motion or piece of union–wide legislation. Moreover, the double–majority principle is discussed from the view–point of voting power distribution. Finally we consider the voting power distribution in a three–chamber system consisting of Commission, Council and EP.