This paper analyzes the welfare implications of information aggregation in a security-trading model where traders have both idiosyncratic endowment risk and asymmetric information about security payoffs. In the model a large market can be welfare-reducing --- i.e., the optimal market size is...

We present a model of excess volatility based on speculation and equilibrium multiplicity. Each trader has two distinct motives to trade: (i) speculation based on noisy signals, and (ii) hedging against endowment shocks. The key to equilibrium multiplicity is the self-fulfilling nature of...