By David Ambler, Matthew Norton
Default rates by municipal bond issuers have been remarkably low over the years. It's an impressive track record, and it explains why defaults by municipal issuers Puerto Rico and Detroit have made front-page news when they happen-they're actually quite rare.
Since 1970, the 10-year cumulative default rate for investment-grade municipal bonds has been 0.1% (Display). Comparing muni default rates with those of investment-grade corporate bonds, which have defaulted at a rate of 2.3%, reinforces the reliability of municipal bonds.
Why is municipal-bond quality so high-and defaults so infrequent?