Risk diversification and extreme risk mitigation

We examine how active risk- and holdings-based diversification of equity portfolios affect performance and vulnerability to large losses. Conducting a comprehensive empirical study of US-based funds, we find that risk-based and sector-based diversification significantly reduce active tail risk and the likelihood of extreme losses, without substantially diminishing portfolio performance. These effects are nonlinear and decreasing, suggesting that investors need not minimizing the concentration of their portfolios. We also examine these relationships on an unprecedented large sample of portfolios using a novel methodology that allows the production of portfolios with similar levels of risk, and find that they are robust to several definitions of extreme risk. Our results highlight the practical value of diversification in managing portfolio risk while maintaining competitive performance.