Do green-themed funds, or other socially-aware and ethical investments, add value or destroy it? Not only do we not know the answer, but we will never know it until the investment industry agrees a common approach to evaluation, according to the French business school Edhec.

Edhec has done a good job of turning itself into a form of "brains trust" for the European institutional asset management industry. Yesterday it unveiled its latest project - a three-year study of the world of environmental, social and ethical funds.