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The gambler's fallacy [Rabin, M. 2002. Inference by believers in the law of small numbers. Quart. J. Econom.117(3) 775–816] predicts that trends bias investor expectations. Consistent with this prediction, we find that investors underreact to streaks of consecutive earnings surprises with the same sign. When the most recent earnings surprise extends a streak, post-earnings-announcement drift is strong and significant. In contrast, the drift is negligible following the termination of a streak. Indeed, streaks explain about half of the post-earnings-announcement drift in our sample. Our results are robust to more general definitions of trends than streaks and a battery of control variables including the magnitude of earnings surprises and their autocorrelation. Overall, post-earnings-announcement drift has a significant time-series component that is consistent with the gambler's fallacy.


This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Management Science, volume 58, issue 7, in 2012 following peer review. The definitive publisher-authenticated version is available online at

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