Look-Ahead Benchmark Bias in Portfolio Performance Evaluation

Posted: 21 May 2019

See all articles by Gilles Daniel

Gilles Daniel

ETH Zürich - Department of Management, Technology, and Economics (D-MTEC)

Didier Sornette

ETH Zürich - Department of Management, Technology, and Economics (D-MTEC); Swiss Finance Institute

Peter Wohrmann

University of Zurich - Swiss Banking Institute (ISB)

Date Written: October 10, 2008

Abstract

Performance of investment managers are evaluated in comparison with benchmarks, such as financial indices. Due to the operational constraint that most professional databases do not track the change of constitution of benchmark portfolios, standard tests of performance suffer from the look-ahead benchmark bias, when they use the assets constituting the benchmarks of reference at the end of the testing period, rather than at the beginning of the period. Here, we report that the look-ahead benchmark bias can exhibit a surprisingly large amplitude for portfolios of common stocks (up to 8% annum for the S&P500 taken as the benchmark) - while most studies have emphasized related survival biases in performance of mutual and hedge funds for which the biases can be expected to be even larger. We use the CRSP database from 1926 to 2006 and analyze the running top 500 US capitalizations to demonstrate that this bias can account for a gross overestimation of performance metrics such as the Sharpe ratio as well as an underestimation of risk, as measured for instance by peak-to-valley drawdowns. We demonstrate the presence of a significant bias in the estimation of the survival and look-ahead biases studied in the literature. A general methodology to test the properties of investment strategies is advanced in terms of random strategies with similar investment constraints.

Keywords: survival bias, look-ahead bias, portfolio optimization, benchmark, investment strategies

JEL Classification: G11, C52

Suggested Citation

Daniel, Gilles and Sornette, Didier and Wohrmann, Peter, Look-Ahead Benchmark Bias in Portfolio Performance Evaluation (October 10, 2008). Swiss Finance Institute Research Paper No. 08-33. Available at SSRN: https://ssrn.com/abstract=1289222 or http://dx.doi.org/10.2139/ssrn.1289222

Gilles Daniel (Contact Author)

ETH Zürich - Department of Management, Technology, and Economics (D-MTEC) ( email )

ETH-Zentrum
Zurich, CH-8092
United States
+41 44 632 8379 (Phone)

HOME PAGE: http://www.er.ethz.ch

Didier Sornette

ETH Zürich - Department of Management, Technology, and Economics (D-MTEC) ( email )

Scheuchzerstrasse 7
Zurich, ZURICH CH-8092
Switzerland
41446328917 (Phone)
41446321914 (Fax)

HOME PAGE: http://www.er.ethz.ch/

Swiss Finance Institute

c/o University of Geneva
40, Bd du Pont-d'Arve
CH-1211 Geneva 4
Switzerland

Peter Wohrmann

University of Zurich - Swiss Banking Institute (ISB) ( email )

Plattenstrasse 14
CH-8032 Zurich, Zurich 8032
Switzerland

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