Linking Credit Risk Premia to the Equity Premium

Abstract

Although the equity premium is - both from a conceptual and empirical perspective - a widely researched topic in finance, there is still no consensus in the academic literature about its magnitude. In this paper, we propose a different estimation method which is based on credit valuations. The main idea is straigtforward: We use structural models to link equity valuations to credit valuations. Based on a simple Merton model, we derive an estimator for the market Sharpe ratio. This estimator has several advantages. First, it offers a new line of thought for estimating the equity premium which is not directly linked to current methods. Second, it is only based on observable parameters. We do neither have to calibrate dividend or earnings growth - which is usually necessary in dividend/earnings discount models - nor do we have to calibrate asset values or default barriers - which is usually necessary in traditional applications of structural models. Third, it is robust to model changes. We examine the model of Duffie/Lando (2001) - which is one of the most sophisticated structural models currently discussed in the literature - to show this robustness. In an empirical analysis we have used CDS spreads of the 125 most liquid CDS in the U.S. from 2003 to 2007 to estimate the equity premium. We derive an average implicit market Sharpe ratio of appr. 40%. Adjusting for taxes and other parts of the credit spread not attributable to credit risk yields an average market Sharpe ratio below 30%. This confirms research on the equity premium, which indicates that the historically observed Sharpe ratio of 40-50% - corresponding to an equity premium of 7-9% and a volatility of 15-20% - was partly due to one-time effects. In addition, our research can be used to explain empirical findings about credit risk premia, which are usually measured as the ratio of risk-neutral to actual default probabilities. We show that the behavior of these ratios can be directly inferred from a simple Merton model and that this behavior is robust to model changes.