In the U.S., momentum portfolios formed on returns from 12 to seven months prior to the current month deliver higher returns than momentum portfolios formed from six to two months prior, suggesting an “echo” in returns (Novy-Marx (2012)). In 37 countries not including the U.S., there is no...

In Merton (1987), idiosyncratic risk is priced in equilibrium as a consequence of incomplete diversification. We modify his model to allow the degree of diversification to vary with average idiosyncratic volatility. This simple recognition results in a state-dependent idiosyncratic risk premium...