Group Size, Group Heterogeneity, and Voting Rules: An Application of the Buchanan-Tullock Model to the European Union

In The Calculus of Consent, Buchanan and Tullock develop a theory of voting rules in which the optimal rule is determined by minimizing the sum of voters' external and decision costs. Other researchers have extended the Buchanan-Tullock model to include the effects of group size and heterogeneity on external and decision costs and, subsequently, on the optimal voting rule. Despite the prominence of the Buchanan-Tullock model in the constitutional, legal, and public-choice literature, their theory has not (to our knowledge) been tested. In this paper we test the Buchanan-Tullock model by examining the establishment and evolution of voting rules in the European Union. Over the past four decades, the European Union has experienced significant changes in number and heterogeneity, and we interpret the general movement towards, and call for, less inclusive voting rules as support for Buchanan and Tullock's original theory.