Structure-Induced Equilibrium

Disequilibrium in collective choice mechanisms based on majority rule has been the subject of much attention in the public choice literature since its discovery by the Marquis de Condorcet in 1785 and more modern treatments by Kenneth Arrow in 1950 and others. This disequilibrium has often been described as cycling, due to the fact that coalition reformation under majority rule can continue through an infinite number of iterations without there emerging a stable coalition—that is to say, a coalition in which the player or players excluded from the winning coalition cannot create a new coalition that will trump the last majority-winning coalition. Theoretical developments have been proposed in an attempt to find solutions to this disequilibrium. For example, Nash equilibrium describes the set of coalition identities where [Page 645]the outcome for each player cannot be improved by unilaterally changing strategy, assuming other players' strategies remained locked.

Aside from these interesting theoretical developments, Gordon Tullock drew attention to the fascinating empirical observation that, despite the theoretical certainty of disequilibrium in majority-rule collective decision making, in practical settings where majority rule is exercised coalitions and preferences remain highly stable. The traditional predictions from public choice theory failed to make sense of this empirical reality. Structure-induced equilibrium is a way of accounting for this inconsistency. If majority rule does not lead to cycling, then it must be the intervention of institutions that prevents such cycling from occurring.

Tullock explains that agenda setters in legislatures—that is, individuals with the power to arbitrate the order of votes—are an example of structure-induced equilibrium because this authority prevents indefinite reiterations of coalition formation and also allows for enforcement of rules of order, such as a prohibition on failed bills receiving repeated attention. Recent studies have explored the presence of structure-induced equilibrium with respect to committee voting and agenda rules in the U.S. Congress.