Using stocks traded on the NYSE, AMEX and NASDAQ for the period of 1964 to 2009, this study demonstrates that, while momentum prevails among small stocks, momentum and reversals coexist among large stocks for a holding period of up to six months. The momentum/reversal divide is along the volatility dimension: Large-cap/low-volatility stocks exhibit reversals while large-cap/high-volatility stocks experience momentum. Our finding is in sharp contrast with those in the existing literature which mostly documents and explains momentum and reversals for different horizons. As such, our study not only offers fresh, new empirical findings on cross-section return predictability but also poses a challenge to the existing theoretical paradigms that are tailored to sequential occurrence of momentum and reversals. Specifically, we contribute to the literature by 1) uncovering a new empirical regularity which explains why large stocks are generally associated with no or weak momentum in the short-term, and 2) advancing a theoretical model based on "moderated confidence" which can rationalize empirical findings such as the one in the current paper where underreaction and overreaction can occur simultaneously with the same investor.

Keywords: momentum, reversals, return predictability, firm size, volatility, moderated confidence, underreaction, overreaction

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