The Systematic Risk of Idiosyncratic Volatility

We show that the pricing of idiosyncratic volatility (IV) is due to unaccounted systematic risk, which affects a large number of asset pricing anomalies. A single common IV component explains one third of variation in IV. Mispricing arises when sorting stocks by the part of IV predicted by exposure to the common IV component, but not when sorting by residual IV. We propose the return difference between stocks with high and low predicted IV, PIV, as a proxy for the missing risk factor. PIV is significantly related to the common components of the returns of several important anomaly-based trading strategies. Controlling for PIV helps explain the earnings surprise, net stock issues, profitability, as well as illiquidity anomalies, and completely explains the financial distress anomaly. Overall our results suggest that the IV puzzle reflects systematic risk related to the average stock volatility and credit risk