The Alphas of Beta and Idiosyncratic Volatility

Abstract

We find that the relation between the idiosyncratic volatility (IVOL) anomaly and the beta anomaly is quite different at long horizons than at short horizons. IVOL has a significantly negative relation with subsequent stock returns at the short horizon of up to six months and beta does not predict stock returns at any horizon. However, both IVOL and beta significantly negatively predict stock alphas over horizons from a few months to beyond one year. At short horizons, neither anomaly can fully explain the other. At long horizons of beyond six months, the IVOL-alpha relation is explained by the beta-alpha relation. A measure of idiosyncratic volatility over a long window, popularly used by the investments industry to construct low-volatility portfolios, behaves similarly to beta in predicting returns and alphas at various horizons, and its predictive power is mostly explained by beta. Overall, IVOL and beta each has unique short-term information, but at long horizons the two anomalies appear to be the same. Our findings help reconcile a perceptional gap between academic studies and the investment industry on low volatility investing, and enrich the debate about the relation between the two low-risk anomalies.

Keywords: Beta anomaly, Idiosyncratic volatility anomaly, alpha

JEL Classification: G11, G12