Issuer-Weighted and Debt-Weighted Default Probabilities

Summary

The document explains two ways to aggregate default rates across a group of issuers. An issuer-weighted rate counts each issuer equally: the share of issuers that default. A debt-volume-weighted rate gives more influence to issuers with more debt outstanding, so it measures the share of debt represented by defaults. The distinction matters because the issuer that defaults may have an above-average or below-average amount of debt.

The example contrasts the two measures for a group of ten issuers: one default produces an issuer-weighted rate of 0.1, while the debt-weighted rate would be higher if that issuer had more debt than average. The document says issuer-level forecasts are Moody’s primary focus, while value-weighted probabilities may better reflect investors whose holdings broadly track debt outstanding. It provides an intuitive distinction, but no estimation procedure, portfolio construction guidance, or treatment of recovery rates and exposure differences.

Key ideas

• Issuer-weighted default probability counts each issuer equally.
• Debt-volume-weighted default probability reflects how much debt is associated with defaulting issuers.
• The two measures can differ when defaulting issuers have atypical debt amounts.
• Issuer-level estimates and debt-weighted measures may serve different analytical needs.

Tags

# Probability of default: issuer vs volume weighted


# Probability of default: issuer vs volume weighted












Some probability of default are issuer-weighted and some are volume-weighted. I don't understand what this means. I had a look into Moody's documentation available here:

https://www.moodys.com/sites/products/ProductAttachments/DRD/CTM_Methodology.pdf

However I still don't understand the part explaining it:

> With the model described in this paper, users are able to forecast the probability of rating transitions and default at the issuer level and at the portfolio level. The portfolio forecast can be equally-weighted across issuers as well as volume weighted.

## Answer by nbbo2 (score 2, accepted)

https://quant.stackexchange.com/a/42907

If there are 10 issuers and one defaults this year, the issuer weighted probability of default is 0.1. But if the one issuer that defaults is one with a larger than average amount of debt outstanding, the dollar volume weighted rate of default for the year is going to be > 0.1.

Moody's tries to predict the default of issuers, so they mostly work with issuer weighted probability of default. But they also provide value weighted probabilities, which may be more relevant to investors who own debt somewhat in proportion to the amount of debt outstanding.

In summary: One is the percentage of issuers that default, the other the percentage of debt that goes bad.

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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.