Now You See It, Now You Don't: The Mysterious Case of the Vanishing Split Bond Rating in States

Abstract

Bond ratings on state‐issued debt provide a signal to credit markets that help them charge an appropriate interest rate, based on the risk of payment default. Though actual default may occur only in extreme circumstances, observed differences in ratings and interest costs across states and time demonstrate that a sound economy, strong financials, and stable policies matter. When data on the factors that presumably affect ratings is public and easily accessible, making sense of differences of opinion between bond rating agencies is difficult. We suggest that such differences—observed as so‐called split bond ratings—are often ephemeral. Utilizing a simulation method to uncover the latent credit risk presented by each state, we show that split ratings on state bonds are often due to the fact that presumed category overlap between rating agencies is absent when evaluated on a common latent scale. Most observed state bond rating splits from 1997 through 2006 can be explained by this category mismatch. Our approach has broad implications for pricing state debt, as well as pricing rated debt in other capital market sectors.