Testing the statistical significance of sector and regional diversification

The question as to whether it is better to diversify a real estate portfolio within a property type across the regions or within a region across the property types is one of continuing interest for academics and practitioners alike. However, this study is somewhat different from the usual sector/regional analysis in that this study is designed to investigate whether a real estate fund manager can obtain a statistically significant improvement in risk/return performance from extending out of a London based portfolio into firstly the rest of the South East of England and then into the remainder of the UK, or whether the manger would be better off staying within London and diversifying across the various property types.

In order to examine these issues we form a number of portfolios that can be directly compared to a number of benchmark portfolios, as well as to each other. Then using the statistical tests developed by Gibbons et al. and Jobson and Korkie, we investigate whether the benefits that accrue from the differing diversification strategies are statistically significant or not.

The results show that staying within only one sector and one region (London) is undesirable in terms of risk and return compared with all three benchmark portfolios considered here. Secondly diversification on a naïve basis, or in an optimal fashion, leads to significant improvements in performance, irrespective of whether it is across different property types within London or within the same sector across the regions. Finally the results indicate that staying within London and diversifying across the various property types may offer performance comparable with regional diversification, although this conclusion largely depends on the time period and the fund manager's ability to diversify efficiently.

The results suggest that diversification almost always offers increased performance. Indeed a little diversification can quickly lead to levels of performance that is superior to number of benchmarks as well as performance insignificantly different from that of the most diversified portfolio that could be constructed! Consequently fund managers should be encouraged to diversify, be it across the regions or across the sectors of the UK.