When Does Idiosyncratic Risk Really Matter?
University of Texas at Dallas - School of Management
February 28, 2010
In contrast to the current literature, we provide new evidence supporting a positive relation between idiosyncratic risk and the expected future market return. Since a large part of the idiosyncratic risk can be diversified away easily, the conventional aggregate idiosyncratic risk measures can only be noisy proxies for the undiversified idiosyncratic risk, which may be priced according to Merton (1987). We thus propose a simple noise reduction method that includes two different noisy measures (dual-predictor) in the same predictive regression to reexamine the relation. We show that the noise effect tends to cancel out in our framework due to the highly correlated noise components of the two measures. In particular, our dual-predictor alone explains future market returns with an adjusted R^2 of 4%. Such a large predictive power is economically significant and robust to the inclusion of other popular predictors and to the choices of sample periods and additional market indices.
Number of Pages in PDF File: 52
JEL Classification: G12, G14, G17
Date posted: February 28, 2010 ; Last revised: September 21, 2010