Price momentum as documented by Jegadeesh and Titman (1993) and earnings momentum as originally documented by Ball and Brown (1968) and later confirmed by Bernard and Thomas (1989) and others are the two prominent anomalies that cannot be explained by the Fama and French (1993) three-factor models. A number of explanations have been proposed to explain these two anomalies, including rational models and behavioral models. Behavioral explanations try to reconcile the anomalies with investor cognitive biases such as investors’ overconfidence and self attribution bias as suggested by Daniel, Hirshleifer and Subrahmanyam (DHS, 1998) and investors’ initial underreaction to new information as suggested by Barberis, Shleifer, and Vishny (BSV, 1998) and Hong and Stein (1999). Rational explanations, however, seek solutions using either the serial correlations in time-varying expected returns or the cross sectional differences in unconditional expected returns. To rationalize the positive serial correlation, Berk, Green, and Naik (1999) develop a model based on optimal asset portfolio decisions of the firm, while Johnson (2002) introduces the growth rate shock that is episodically persistent. From a different perspective, Conrad and Kaul (1998) find a nontrivial role of cross sectional dispersion in mean returns and use this finding to justify that momentum profits are attributable to risk.
Given the fact that realized returns can be decomposed by an expected return component and a return innovation component (i.e., an unexpected return component), return decomposition may provide a framework in which different explanations can be potentially tested. If the expected return component plays a dominant role in explaining momentum profits, momentum profits are more consistent with the risk-based explanation. In contrast, if the return innovation component plays a dominant role in explaining momentum profits, then momentum profits might be more consistent with the behavioral justification.