We investigate the effect of line-of-business diversification on asset risk-taking in the U.S. property-liability industry. The coordinated risk management hypothesis (Schrand and Unal, 1998) implies a negative relation between underwriting risk and investment risk. Consistent with this hypothesis we find that diversified insurers take more asset risk than non-diversified insurers, and that the degree of asset risk-taking is positively related to diversification extent. Our results are robust to corrections for potential endogeneity bias, selectivity bias, and alternative diversification and asset risk measures. We also provide event study evidence that further supports the coordinated risk management hypothesis. Specifically, we find that when a focused firm diversifies, it increases its asset risk relative to firms that remain focused, and when a diversified firm refocuses, it reduces its asset risk relative to firms that remain diversified.

Investors may underdiversify their portfolios by overweighting securities in which they perceive an informational advantage or by underweighting securities to hedge risks outside the portfolio. We investigate underdiversification in institutional portfolio construction by examining the under/overweighting of industries in U.S. property–liability (PL) insurers’ equity portfolios. We find that PL insurers underweight both their own industry and highly correlated industries in their portfolios. This underweighting is larger for PL insurers exposed to higher underwriting risk. Although PL insurers have an informational advantage in investing in their peers, their underwriting risk drives them to underweight stocks in their industry.