Exploring the relationship between credit spreads and default probabilities

Mark J. Manning

"Contrary to theory, recent empirical work suggests that changing default expectations can explain only a fraction of the variability in credit spreads. This paper takes a fresh look at this question, relating credit spreads for a sample of investment-grade bonds issued by UK industrial companies to default probabilities generated by the Bank of England's Merton model of corporate failure. For the highest quality corporate issues, where the probability of default is low, this factor explains relatively little of the variation in credit spreads. For such bonds, common market factors - perhaps related to liquidity conditions - appear to be of greater importance. This is consistent with previous empirical work. For lower-rated investment-grade bonds, however, the probability of default is found to be a more important determinant of credit spreads, explaining around a third of variability...