Toward the Design of Better Equity Benchmarks

Abstract

Following recent research on the relevance of idiosyncratic risk in asset pricing models, the author proposes using total volatility as a model-free estimate of a stock's excess expected return and analyzes the implications, in terms of design, for improved equity benchmarks. The author finds that maximum Sharpe ratio portfolios are consistent with such expected return proxies and, if built upon improved estimates of the correlation parameters, will significantly outperform market cap–weighted schemes on a risk-adjusted basis. This analysis, which rehabilitates the role of the tangency portfolio from modern portfolio theory, suggests that better equity benchmarks can be designed, provided that a sophisticated portfolio optimization procedure is used that relies on robust estimates of moments and co-moments of stock return distributions. The article has important potential implications for the on-going debate about appropriate weighting schemes for equity indices.