Time-Varying Index Benchmarks for Mutual Fund Alpha Evaluation
Summary
The document examines how benchmark choice affects mutual fund performance estimates. It contrasts return-based evaluation, which is sensitive to benchmark selection, with holdings-based evaluation, which can be more precise but depends on infrequently available portfolio disclosures. It also argues that factor and index benchmarks are not interchangeable when common risk factors are omitted, since factor regressions may then attribute risk compensation to alpha.
The proposed method uses a regime-switching model estimated by maximum likelihood and an expectation-maximization procedure to select among 17 passive US equity indexes over time, optionally including cash or adjusting for cash exposure. In historical US mutual fund data, the selected benchmarks better captured fund styles and reduced unexplained factor exposures; they also improved identification of statistically significant alpha and showed stronger out-of-sample alpha persistence than fixed alternatives. The evidence is historical and US-focused, and the benchmarks are inferred after the fact, which limits their use as ex ante standards. The source summarizes a study rather than offering an independently reproduced test.
Key ideas
- Benchmark mismatch can increase the variance of estimated mutual fund alpha.
- Factor benchmarks may overstate alpha when omitted common risks carry positive compensation.
- A regime-switching model can identify changing index benchmarks from fund returns without holdings data.
- Accounting for cash exposure can improve how well benchmarks capture fund risk and style.
- The reported out-of-sample persistence advantage comes from historical US fund data and may not generalize.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.