DO U.S. STOCK MARKET INDEXES OVER‐ OR UNDERREACT?

Abstract

Abstract Our objective is to investigate the short‐term over‐ or underreaction of six U.S. stock market indexes. We find evidence of a one‐day underreaction for winners (days on which an index experiences abnormally high returns) and losers (days on which an index experiences abnormally poor performance). We also find strong evidence of a sixty‐day underreaction for winners. For losers, abnormal returns turn from negative to positive as the period is extended, resulting in significant reversals over the sixty‐day period. Results are generally consistent for each of the six indexes. Overall, these results provide strong support for the uncertain information hypothesis. JEL classification: G14