The Prudent Investor Rule and Market Risk: An Empirical Analysis

Abstract

The prudent investor rule, enacted in every state over the last 30 years, is the centerpiece of fiduciary investment law. Repudiating the prior law's emphasis on avoiding risk, the rule reorients fiduciary investment toward risk management in accordance with modern portfolio theory. The rule directs trustees to implement an overall investment strategy having risk and return objectives reasonably suited to the trust. Using data from reports of bank trust holdings and fiduciary income tax returns, we examine trustee management of market risk before and after the reform. First, we find that the reform increased stock holdings only among banks with average trust account sizes above the 25th percentile. This result is consistent with sensitivity in asset allocation to beneficiary risk tolerance as proxied by account size. Second, we find that, although stockholdings increased after the reform, trust corpus did not become more correlated with the market. We explain this result in part with evidence of increased portfolio rebalancing after the reform. We conclude that the rule’s command to align market risk with beneficiary risk tolerance, and to manage market risk exposure on an ongoing basis, has largely been followed.