Do Sunspots Matter?
研究外在不确定性（如“动物精神”、“市场心理”）在理性预期均衡模型中是否重要。在静态完全市场模型中不重要，但在世代交叠模型中，即使市场完全，只要参与限于当期存活者，外在不确定性就能影响均衡。
Can extrinsic uncertainty ("animal spirits," "market psychology," "sunspots,"...) play a significant role in rational expectations equilibrium models? We establish that extrinsic uncertainty cannot matter in the static Arrow-Debreu economy with complete markets. But we also establish that extrinsic uncertainty can matter in the overlapping-generations economy with complete markets but where market participation is limited to those consumers alive when the markets are open. Equilibrium allocations in which extrinsic uncertainty plays no role are Pareto optimal in the traditional sense. Equilibrium allocations in which extrinsic uncertainty does play a role are Pareto optimal in a (weaker) sense which is appropriate to dynamic analysis.