A theoretical fight is raging in the financial journals about the best way to compile an index. The argument between the proponents of the capitalisation-weighted indices and supporters of fundamentally weighted ones is abstruse, but could undermine the efficient markets hypothesis, the underpinning of most current financial theory.

Whether or not the debate might yield something useful to investors is a separate issue that has not had so much attention in the storm over models, theory, data-mining, optimality and fair value.