Modern Portfolio Theory Faces Issues As Correlations Turn Positive




However, Modern Portfolio Theory may have a problem going forward. Don’t worry, we are not going to hack on bonds based on a fear that yields may rise in the future, creating a portfolio drag. There are already enough bond haters out there. The issue we are seeing goes beyond just the bond argument – correlations have been rising just about everywhere. In today’s world, correlations have been changing, with more and more asset classes becoming increasingly correlated. The problem: when the correlations between investments are higher, it becomes harder to diversify risk in a portfolio.

Let’s start with the big one, global bonds and global equities. Combining equities and bonds has benefitted from a generally negative correlation for much of the past few decades. However, this correlation has turned positive of late (chart 1), implying reduced diversification benefits when combining bonds and equities. This isn’t too much of a concern, given that the long-term average is slightly positive.

But don’t throw out your bonds just yet. This correlation tends to return to be strongly negative during risk-off periods in the equity markets. This reflex action during corrections helps maintain bonds in portfolios, even if they experience periods of low or even negative performance.

Publication Date: 15 Sept 2021

Publication Site: The Wealth Advisor