Portfolio Constraints and the Fundamental Law of Active Management

43 Pages Posted: 14 Nov 2001

See all articles by Steven Thorley

Steven Thorley

BYU Marriott School of Business

Multiple version iconThere are 2 versions of this paper

Date Written: November 2001


Active portfolio management is typically conducted within constraints that do not allow managers to fully exploit their ability to forecast returns. Constraints on short positions and turnover, for example, are fairly common and materially restrictive. Other constraints, such as market-cap and value/growth neutrality with respect to the benchmark, or economic sector constraints, can further restrict an active portfolio's composition. We derive ex-ante and ex-post correlation relationships that facilitate constrained portfolio performance analysis. The ex-ante relationship is a generalized version of Grinold's (1989) fundamental law of active management, and provides an important strategic perspective on the potential for active management to add value. The ex-post correlation relationships represent a practical decomposition of performance into the success of the return prediction process and the noise associated with portfolio constraints. We verify the accuracy of these relationships with a Monte-Carlo simulation and illustrate their application with equity portfolio examples based on the S&P 500 benchmark.

Keywords: Portfolio Constraints, Fundamental Law of Active Management, Information Ratio

JEL Classification: G11

Suggested Citation

Thorley, Steven, Portfolio Constraints and the Fundamental Law of Active Management (November 2001). Available at SSRN: https://ssrn.com/abstract=290916 or http://dx.doi.org/10.2139/ssrn.290916

Steven Thorley (Contact Author)

BYU Marriott School of Business ( email )

616 TNRB
Brigham Young University
Provo, UT 84602
United States
801-378-6065 (Phone)
801-378-5984 (Fax)

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