On the typicality of the representative agent

The aim of this paper is to explore under which conditions a representative agent (RA) model is able to correctly approximate the output of a more realistic model based on the "true" assumption of many interacting agents. The starting point is the widespread Keynesian cross diagram, which is compared to an extended versions that explicitly considers a multiplicity of interacting households and firms, and collapses into the original model when the number of agents is one per type. Results show that the RA Keynesian cross diagram model is not a good approximation of the extended model when (i) the network structure of the economy is not symmetric enough, e.g. firms have different sizes, or (ii) the rationality of agents is not high enough. When income inequality is considered, through the introduction of capitalists, the representative agent model is no more a good approximation, even if the agents are rational. A fiscal policy that targets income redistribution improves the prediction of the RA model. In general, all features that increase overall rationality in the economy and decrease its heterogeneity, tend to improve the performance of the RA approximation.