Correlation and Portfolio Performance

August 31, 2015  | By Kevin Smith

Different types of investments are subject to different types of risk. On days when you notice that stock prices have fallen, for example, it would not be unusual to see a rally in the bond market.

Asset allocation refers to how an investor’s portfolio is divided among asset classes, which tend to perform differently under different market conditions. An appropriate mix of investments typically depends on the investor’s age, risk tolerance, and financial goals.

The concept of correlation often plays a role in constructing a well-diversified portfolio that strikes a balance between risk and return.

Math that matters

In the financial world, correlation is a statistical measure of how two securities perform relative to each other. Securities that are positively correlated will have prices that tend to move in the same direction. Securities that are negatively correlated will have prices that move in the opposite direction.

A correlation coefficient, which is calculated using historical returns, measures the degree of correlation between two investments. A correlation of +1 represents a perfectly positive correlation, which means the investments always move together, in the same direction, and at a consistent scale. A correlation of -1 means they have a perfectly negative correlation and will always move opposite one another. A correlation of zero means that the two investments are not correlated; the relationship between them is random.

In reality, perfectly positive correlation is rare, because distinct investments can be affected differently by the same conditions, even if they are similar securities in the same sector.

Correlations can change

While some types of securities exhibit general trends of correlation over time, it’s not uncommon for correlations to vary over shorter periods. In times of market volatility, for example, asset prices were more likely to be driven by common market shocks than by their respective underlying fundamentals.

During the flight to quality sparked by the financial crisis of 2008, riskier assets across a number of different classes exhibited unusually high correlation. As a result, correlations among some major asset classes have been more elevated than they were before the crisis. There has also been a rise in correlation between different financial markets in the global economy.¹ For example, the correlation coefficient for U.S. stocks (represented by the S&P Composite Total Return index) and foreign stocks (represented by the MSCI EAFE GTR index) increased from 0.75 over the last 25 years to 0.89 over the last 10 years.²

Over the long run, a combination of investments that are loosely correlated may provide greater diversification, help manage portfolio risk, and smooth out investment returns. Tighter relationships among asset classes over the last decade may be a good reason for some investors to reassess their portfolio allocations. However, it’s important to keep in mind that correlations may continue to fluctuate over time because of changing economic and market environments.

The performance of an unmanaged index is not indicative of the performance of any particular investment. Individuals cannot invest directly in an index. Past performance is no guarantee of future results. All investing involves risk, including the possible loss of principal. Asset allocation and diversification strategies do not guarantee a profit or protect against investment loss; they are methods used to help manage investment risk.

Investing internationally carries additional risks such as differences in financial reporting, currency exchange risk, as well as economic and political risk unique to the specific country. This may result in greater share price volatility. When sold, investments may be worth more or less than their original cost.

¹International Monetary Fund, 2015

²Thomson Reuters, 2015, for the period 12/31/1989 to 12/31/2014