How Mutual Fund Portfolio Concentration Relates to Risk-Adjusted Performance

Summary

This study examines whether active U.S. equity mutual funds that increase portfolio concentration subsequently achieve better risk-adjusted performance. Its rationale is a tradeoff: concentrating holdings can give greater weight to the manager’s strongest ideas and raise expected alpha, while increasing idiosyncratic volatility and trading costs. The study measures concentration mainly with a benchmark- and quarter-adjusted Herfindahl index, and evaluates performance using factor-model alpha and its t-statistic.

Using quarterly observations from 1999–2014, the authors find that within-fund increases in concentration predict higher subsequent risk-adjusted performance, though the estimated alpha effect is modest. The association is stronger for funds with lower institutional ownership and in conditions such as low investor sentiment or market liquidity, consistent with managers needing more valuable information to justify added concentration when its costs rise. Results are generally positive across alternative concentration measures and benchmarks, but vary across performance models. The findings are observational and do not imply that all funds would benefit from concentrating more; they concern managers’ choices and subsequent outcomes.

Key ideas

• Concentrated portfolios can raise expected alpha while also increasing idiosyncratic risk and trading costs.
• Within-fund increases in concentration are associated with stronger subsequent risk-adjusted performance.
• The relationship is stronger in some fund and market conditions that may raise the costs of concentration.
• Results are broadly robust to alternative measures, though their strength depends on the performance model.
• The evidence does not establish that concentration increases would benefit mutual funds as a group.

Tags

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