The Price Impact and Survival of Irrational Traders

Milton Friedman argued that irrational traders will consistently lose money, won’t survive and, therefore, cannot influence long run equilibrium asset prices. Since his work, survival and price influence have been assumed to be the same. Often partial equilibrium analysis has been relied upon to examine the survival of irrational traders and to make inferences on their influence on prices. In this paper, we demonstrate that survival and influence on prices are two independent concepts. The price impact of irrational traders does not rely on their long-run survival and they can have a significant impact on asset prices even when their wealth becomes negligible. In addition, in contrast to a partial equilibrium analysis, general equilibrium considerations matter since the ability of irrational traders to impact prices even when their wealth is diminishing can significantly affect their chances for long-run survival. In sum, in a long-run equilibrium, we explicitly show that price impact can occur whether or not the irrational traders survive. In related work, we show that even if the irrational traders survive they may have no price impact. The authors thank Ming Huang, Wei Xiong and participants of the 2002 NBER Asset Pricing Summer Conference, the 2003 Meeting of the Econometric Society, and seminars at LBS, MIT, NYU and University of Minnesota for valuable comments. Sloan School of Management, MIT, Cambridge, MA 02142 and NBER. Sloan School of Management, MIT, Cambridge, MA 02142 and NBER. Sloan School of Management, MIT, Cambridge, MA 02142, CCFR and NBER. Department of Economics, MIT, Cambridge, MA 02142.