Abstract We consider a pure exchange economy with incomplete information. Some agents display learning bias and over- or under-react to the arrival of new information. We show under which conditions biased agents survive over a finite horizon. We also study the distribution of irrational agents consumption shares. Irrational agents have a signiÞcant consumption share in the economy when (i) shocks are less persistent (ii) risk aversion is high (iii) volatility of aggregate consumption is high. We also show that agents impact on prices is increasing in their consumption share and conclude that biased agents can signiÞcantly influence equilibrium quantities.

When investors have incomplete information, expected returns, as measured by an econometrician, deviate from those predicted by standard asset pricing models by including a term that is the product of the stock’s idiosyncratic volatility and the investors’ aggregated forecast errors. If investors are biased this term generates a relation between idiosyncratic volatility and expected stocks returns. Relying on forecast revisions from IBES, we construct a new variable that proxies for this term and show that it explains a significant part of the empirical relation between idiosyncratic volatility and stock returns.

The representative-agent Lucas model stresses aggregate risk and hence does not allow us to study the impact of agents’ heterogeneity on the dynamics of equilibrium trading volume. In this paper, we investigate under what conditions non-informational heterogeneity, i.e., differences in preferences and endowments, leads to nontrivial trading volume in equilibrium. We present a non-informational no-trade theorem that provides necessary and sufficient conditions for zero equilibrium trading volume in a continuous-time Lucas market model with heterogeneous agents, multiple goods, and multiple securities. We explain in detail how no-trade equilibria are related to autarky equilibria, portfolio autarky equilibria, and peculiar financial market equilibria, which play an important role in the literature on international risk sharing.