When Bond Fund NAV Data Can Estimate Portfolio Duration

Summary

The document compares two ways to estimate a bond fund’s duration. A holdings-based estimate builds a proxy portfolio from the largest positions disclosed in periodic reports and calculates its weighted duration. A NAV-based estimate regresses the fund’s net asset value time series on factors; exposure to the level factor is used to indicate relative duration. The study treats the holdings estimate as a benchmark and judges NAV estimates by their correlation with it.

The reported findings suggest that NAV-based estimates are less reliable overall and can differ substantially from holdings-based results. They appear more effective when a fund holds a larger share of bonds and a smaller share of equities or convertible bonds, and when more of its bonds trade on exchanges. The authors also report differences across fund companies. They propose that equity volatility can obscure fixed-income exposures and that interbank bond pricing practices may weaken the relationship between NAV movements and market factors. Fund size, size volatility, credit exposure, and leverage show no significant relationship with estimation quality in the analysis. The summary provides no sample details or numerical results, and its correlations do not establish causation.

Key ideas

• The holdings method estimates duration from a weighted proxy portfolio built from disclosed major bond positions.
• The NAV method uses factor exposures, with level-factor exposure serving as a relative duration indicator.
• NAV estimates often diverge from holdings estimates, which the study assumes are the more reliable benchmark.
• High equity and convertible-bond allocations are associated with poorer NAV-based duration estimates.
• A greater share of exchange-traded bonds is associated with better agreement between the two methods.

Tags

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