On Aggregation and Representative Agent Equilibria

Aggregation is an often used tool in finance and macroeconomics, whereby economic equilibrium in a heterogeneous trader economy is characterized by means of the first order optimality conditions of a representative agent. In this paper we study the conditions under which a representative agent exists, and investigate the implications for the existence of equilibrium. The approach applies to markets which are incomplete, including markets with trading constraints, heterogeneous beliefs, and differential information