Momentum Loses Its Momentum: Implications for Market Efficiency

We evaluate the robustness of momentum returns in the US stock market over the period 1965 to 2010. We find that momentum profits have become insignificant since the late 1990s partially driven by pronounced increase in the volatility of momentum profits in the last 12 years. Past returns no longer explain the cross-sectional variation in stock returns, not even following up markets. The patterns in the post holding period returns of momentum portfolios and risk adjusted identification period buy and hold returns of stocks in momentum supports improvement in market efficiency as a possible explanation for the declining momentum profits.