Understanding the nature of the risks and the source of the rewards to momentum investing

Buying recent winners and shorting recent losers guaranteestime-varying factor exposures in accordance with the performanceof common risk factors during the ranking period. Adjusted forthis dynamic risk exposure, momentum profits are remarkablystable across subperiods of the entire post-1926 era. Factormodels can explain 95% of winner or loser return variability,but cannot explain their mean return components are more profitablethan those based on total returns. Neither industry effectsnor cross-sectional differences in expected returns are theprimary cause of the momentum phenomenon.