Finally, Hong and Stein (1999) present a model populated by “news watchers,” those who base their trades
on private information but not past prices, and “momentum traders,” those who base their trades on past price
trends. News spreads slowly among the news watchers, causing initial underreaction, but it is followed by
momentum buying that can create an eventual overreaction.
Related empirical work includes Dreman and Berry’s (1995) study that finds an asymmetry of response to
earnings surprise between low and high P/E stocks. Low P/E (i.e., value) stocks respond most favorably to a positive
earnings surprise, suggesting the low P/E status may be the result of prior overreaction to negative news. Lee and
Swaminathan (2000) show that turnover levels provide a link between value and momentum effects. Winners with
high past volume experience reversals at five-year horizons, consistent with initial underreaction and eventual
overreaction. They argue also that as stocks decline in popularity, trading volume drops off and the stocks become
neglected value stocks. Taffler, Lu, and Kausar (2004) document market underreaction to the bad news contained
in going-concern-modified audit reports. The underreaction may be the result of the limits to arbitrage in the
sample companies, predominantly small loser stocks, but the authors cannot rule out the behavioral explanation of
investors (professional and individual) being in denial of the implications of the going-concern opinion.
Other articles attempt to explain short-term momentum in returns, arguably the most difficult empirical
finding to reconcile with traditional rational finance theory. Grinblatt and Han (2005) argue that prospect theory,
and the resulting tendency of investors to hold losing positions and sell winners, explains the momentum effect.
This trading behavior of investors means prices underreact to news and momentum occurs as the mispricing slowly
corrects. For example, when good news emerges about a stock, selling by investors who, subject to the disposition
effect, are inclined to sell winners will slow the pace at which the good news can be reflected in a higher stock
price. The authors find that a proxy for unrealized gains, which will determine investors’ disposition to sell or
hold, can explain the level of momentum profits.
Representativeness Bias and “Good
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