One of the first and most influential papers in the overreaction category is DeBondt and Thaler ( 1985), who find that stock returns are negatively correlated at long horizons. Specifically, stocks that have had the lowest returns over any given five year period tend to have high returns over the subsequent five years, and vice versa. A common interpretation of this result is that when there is a sustained streak of good news about an asset, its price overshoots its " fundamental value", and ultimately must experience a correction. More recent work in the same spirit has continued to focus on long horizon predictability, but has used what are arguably more refined indicators of fundamental value, such as book-to-market and cashflow-to-price ratios ( Fama and French 1992, lakonishok, Shleifer and Vishny 1994).The underreaction evidence can be decomposed along the following lines. First, returns tend to exhibit unconditional positive serial correlation at short horizons on the order of six to twelve months. This is true both for aggregate indices ( Cutler, Poterba and Summers 1991) and in cross-sections of individual stocks ( Jegadeesh and Titman 1993 ). One possible interpretation of this unconditional evidence, which fits most closely with the spirit of the model we develop below is that information which is intially private is incorporated into prices only gradually. Second, conditional on observable public events, stock tend to experience post-event drift in the same direction as the initial event impact. The types of events that have been examined in detail and that fit this pattern include: earnings announcements, stock issues and repurchases, dividend initiations and omission, and analyst recommendations. Recent work by Chan, Jegadeesh and Lakonishok ( 1996) shows that these two types of underreaction are distinct: ina multiple regression, both past returns and public earnings surprises help to predict subsequent returns at horizons of six months and one year. This seems to suggest that the market underreacts to both information which is initially private, as well as information which is made publicly available to all investors simultaneously
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