TY - JOUR AU - Dumas,Bernard AU - Kurshev,Alexander AU - Uppal,Raman TI - What Can Rational Investors Do About Excessive Volatility and Sentiment Fluctuations? JF - National Bureau of Economic Research Working Paper Series VL - No. 11803 PY - 2005 Y2 - November 2005 UR - http://www.nber.org/papers/w11803 L1 - http://www.nber.org/papers/w11803.pdf N1 - Author contact info: Bernard Dumas INSEAD boulevard de Constance 77305 Fontainebleau Cedex FRANCE Tel: +33 1 60 72 43 73 Fax: +33 1 60 72 40 50 E-Mail: bernard.dumas@insead.edu Alexander Kurshev London Business School E-Mail: akurshev.PHD2003@london.edu Raman Uppal EDHEC Business School 10 Fleet Place, Ludgate London EC4M 7RB United Kingdom Tel: +44 20 7871 6740 E-Mail: ruppal@mac.com AB - Our objective is to understand the trading strategy that would allow an investor to take advantage of "excessive" stock price volatility and "sentiment" fluctuations. We construct a general equilibrium model of sentiment. In it, there are two classes of agents and stock prices are excessively volatile because one class is overconfident about a public signal. This class of irrational agents changes its expectations too often, sometimes being excessively optimistic, sometimes being excessively pessimistic. We find that because irrational traders introduce an additional source of risk, rational investors reduce the proportion of wealth invested into equity except when they are extremely optimistic about future growth. Moreover, their optimal portfolio strategy is based not just on a current price divergence but also on a prediction concerning the speed of convergence. Thus, the portfolio strategy includes a protection in case there is a deviation from that prediction. We find that long maturity bonds are an essential accompaniment of equity investment, as they serve to hedge this "sentiment risk." The answer to the question posed in the title is: "There is little that rational investors can do optimally to exploit, and hence, eliminate excessive volatility, except in the very long run." ER -