Improved investment performance using the portfolio diversification index

The residual variance method is the traditional method for measuring portfolio diversification relative to a market index. Problems arise, however, when the market index itself is not appropriately diversified. A diversification measurement (Portfolio Diversification Index), free from market index influences, has been recently introduced. This article explores whether this index is a robust and ‘good’ diversification measure compared with the residual variance method. South African unit trusts are diversification-ranked using the two measures and the results compared to the ranking results of several risk performance measures. Measuring relative concentration levels allows concentration risk to be effectively managed, thereby filling a gap in the Basel accords (which omit concentration risk).