Stock Market Index - Criticism of Capitalization-weighting

Criticism of Capitalization-weighting

The use of capitalization-weighted indices is often justified by the central conclusion of modern portfolio theory that the optimal investment strategy for any investor is to hold the market portfolio, the capitalization-weighted portfolio of all assets. However, empirical tests conclude that market indices are not efficient. This can be explained by the fact that these indices do not include all assets or by the fact that the theory does not hold. The practical conclusion is that using capitalization-weighted portfolios is not necessarily the optimal method.

As a consequence, capitalization-weighting has been subject to severe criticism (see e.g. Haugen and Baker 1991, Amenc, Goltz, and Le Sourd 2006, or Hsu 2006), pointing out that the mechanics of capitalization-weighting lead to trend-following strategies that provide an inefficient risk-return trade-off.

Also, while capitalization-weighting is the standard in equity index construction, different weighting schemes exist. First, while most indices use capitalization-weighting, additional criteria are often taken into account, such as sales/revenue and net income (see the “Guide to the Dow Jones Global Titan 50 Index”, January 2006). Second, as an answer to the critiques of capitalization-weighting, equity indices with different weighting schemes have emerged, such as "wealth"-weighted (Morris, 1996), “fundamental”-weighted (Arnott, Hsu and Moore 2005), “diversity”-weighted (Fernholz, Garvy, and Hannon 1998) or equal-weighted indices.