"This paper finds strong evidence of time-variations in the joint distribution of returns on a stock market portfolio and portfolios tracking size--and value effects. Mean returns, volatilities and correlations between these equity portfolios are found to be driven by underlying regimes that...

We show that firms' idiosyncratic volatility obeys a strong factor structure and that shocks to the common factor in idiosyncratic volatility (CIV) are priced. Stocks in the lowest CIV-beta quintile earn average returns 5.4% per year higher than those in the highest quintile. The CIV factor...