Groupe d’études et de recherche en analyse des décisions

Stability and Stability Index of Political Mechanisms

Joseph Abdou Université Paris 1, France

Stability is an essential requirement for political institutions; however it is both a theoretical and an empirical fact that political institutions are often unstable. Stability depends on the notion of solution adopted for the game. Instability occurs when contradictory forces prevent the emergence of a persistent outcome. We study in a general setting the stability and the stability index related to the core solution. Moreover we consider a special mechanism namely the meet game form defined on a meet-semilattice and we show that the stability index relative to the equilibrium, to the beta core and to the exact core is a function of the Nakamura number, the depth of the semilattice and its gap function.