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Much of the market's annual premium occurs on a few days on which several of the market's most famous firms simultaneously announce earnings after the close. The effect is a pre-announcement drift whereby prices rise before announcements.

Authors: Yixin Chen, Randolph B. Cohen, Zixuan Wang

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In this research, the authors show that much of the market premium for the year occurs on a handful of days, identifiable well in advance, on which several of the market’s most famous, high-media-attention firms simultaneously announce earnings after the market close. Puzzlingly, the market surges occur during the 24 hours prior to the earnings announcements, from close to close. Since there is no overlap between the price increase period and the information revelation, the high returns do not appear to represent a risk premium, and the tests seem to rule out information-leakage explanations. Deepening the puzzle, the market delivers high returns only prior to post-close earnings-announcement clusters, not in advance of clusters that occur in the pre-open period. In addition to being economically large and easily tradeable, the effect is statistically significant, and the results hold consistently throughout our sample. They argue that the best explanation for their findings is that of Miller (1977) as extended by Hong and Stein (2007): when over a short “attention” period difference of opinion combines with short-sale constraints, prices will rise as optimists buy while pessimists cannot sell.


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