Guo, Hui, Robert Savickas, Zijun Wang, and Jian Yang
Journal of Financial and Quantitative Analysis, Vol 44, Issue 1 , pp. 133-154

Recent authors argue that the value premium constructed from the cross-section of stocks is a proxy for investment opportunities. We show that this conjecture sheds light on the puzzling empirical risk-return tradeoff in the stock market across time. That is, in contrast with many early authors, we find that the stock market return is positively and significantly related to its conditional variance after controlling for its covariance with the value premium. The covariance, which is negatively correlated with stock variance, is positively and significantly priced as well.

Therefore, by ignoring the effect of time-varying investment opportunities on the stock market return, the early specification might suffer from an omitted variables problem, which generates a downward bias in the estimate of the risk-return relation. Also, consistent with recent investment-based equilibrium models, we document a positive and significant relation between the value premium and its conditional variance over the post-1963 period. Overall, our empirical evidence suggests that the value premium might be a proxy for investment opportunities.