Instability and Convergence Under Simple-Majority Rule: Results from Simulation of Committee Choice in Two-Dimensional Space

Nondeterministic models of collective choice posit convergence among the outcomes of simple-majority decisions. The object of this research is to estimate the extent of convergence of majority choice under different procedural conditions. The paper reports results from a computer simulation of simple-majority decision making by committees. Simulation experiments generate distributions of majority-adopted proposals in two-dimensional space. These represent nondeterministic outcomes of majority choice by committees. The proposal distributions provide data for a quantitative evaluation of committee-choice procedures in respect to outcome convergence. Experiments were run under general conditions, and under conditions that restrict committee choice to several game-theoretic solution sets. The findings are that, compared to distributions of voter ideal points, majority-adopted proposals confined to the solution sets demonstrate different degrees of convergence. Second, endogenous agenda formation is a more important obstacle to convergence than the inherent instability of simple-majority rule. Third, if members maximize preferences in respect to agenda formation, a committee choice that approximates the central tendency of the distribution of voter preferences is unlikely. The conclusion is that the most effective way to increase the convergence of majority choice is to restrict the role of individual preferences in agenda formation: identification of proposals to be voted up or down by a committee. This revised version was published online in June 2006 with corrections to the Cover Date.