Critics on Gary Brinson' Theory

If global investing is superior to investing in only one market, why do so many investors hold disproportionate amounts of their portfolios in equities of their own domestic markets? Even sophisticated institutional investors, such as pension funds and insurance companies, tend to concentrate well over three-quarters of their equity funds in domestically quoted shares, a phenomenon known as home bias. Evidence of wide discrepancies between national market performances over certain periods of time suggests that these investors would maximize their returns and minimize their risks more effectively by diversifying more fully across stocks in different countries.

Various explanations for home bias have been advanced. These include IMF officials' arguments that it is, in large part, due to the substantial risks of adverse exchange rate changes, which cannot be guarded against with standard hedging techniques. Currency risks may be compounded by the different supervisory environments in particular markets, by fears that capital controls may be instituted, by taxes on international trading or simply by a wish to avoid the time and expense of maintaining and researching a more widely spread international portfolio.

Such reasoning is supported by arguments that the benefits of international diversification arise merely from the fact that different stock markets have their shares concentrated in different industries. For example, the UK privatization program of the 1980s means that utilities are a more important part of the London market than elsewhere. Similarly, investment in the Swiss market implies a disproportionate bet on banking stocks, and investment in the Swedish market a commitment to basic industries. The implication is that global investing offers nothing more than exposure to additional industries.

Yet home bias on the part of institutional investors seems to be more a result of government restrictions on the amount of foreign assets pension funds and insurance companies in any given country are allowed to hold. It also may arise from the way in which fund managers' performance is assessed through reference to a local market index: even if passive indexing is not their dominant strategy, there is inevitably a strong incentive to own a good slice of the index's components. And industry analysts are often more prevalent than country analysts in fund managers' offices, suggesting a disposition to choose industrial over international diversification.

There is evidence that the covariances of global markets may be sliding closer, though Japan may be a special case. For the other members of the G-7, coordinated banking policies and facilitated information flows should tend to drive markets into a more steady alignment. On the surface, such an increase in stability could be seen as beneficial for business but would be a lessened benefit for portfolio investors attempting to diversify risk.

For example, closer links between European economies following the introduction of the euro will increase the incentive for US investors to diversify into European markets. At the same time, this may also strengthen the relationship between different European stock markets, reducing the incentive for diversification within Europe.