Rick Bookstaber’s post today deserves a read. This bit on diversification captures the flavor of his comments:
Diversification works well, except when it really matters
We all know the argument from Finance 101: If you hold 16 uncorrelated assets, your risk will drop by a factor of four. Well good luck with that.
During a crisis, when diversification really matters, correlations aren’t near zero (as if they ever are). All that people care about is risk and liquidity. All assets that are highly risky drop, all assets that are less liquid drop. No one cares about the subtlety of earnings streams. It is like high energy physics. When the heat gets turned up high enough, matter is just matter, the distinctions between the elements is blurred away.
This is not to say that one should not try to diversify, but rather that one should not think diversification will work magic. It is a given that a portfolio should not be limited to U.S. Treasuries and S&P 500 stocks, because while it should not be oversold, diversification does have some benefit. And, on the other side, unless someone is still living in the 1970â€™s, it borders on the intellectually dishonest to trumpet a diversified portfolio by using the S&P 500 as the bogey. A college kid can construct a portfolio that will beat the S&P 500 on a risk-adjusted basis, because there are so many more markets available now. A better approach is to look at a given asset allocation versus its nearby well-diversified neighbors, and try to understand why one is better than the other.
[From Asset Allocation]