Correlation is a statistical measure that quantifies how two investments move in relation to each other. It ranges from -1 to +1: a correlation of +1 means assets move perfectly together, -1 means they move in opposite directions, and 0 means their movements are completely independent. Understanding correlation is essential for building a resilient investment portfolio.
How It Works
Correlation measures the strength and direction of a relationship between two asset price movements. When you calculate correlation, you're examining historical price data to determine whether assets tend to rise and fall together or separately. A positive correlation means that when one asset increases, the other tends to increase as well. A negative correlation means they tend to move in opposite directions. This relationship is expressed as a number between -1 and +1, with zero indicating no consistent relationship.
For example, tech stocks and biotech stocks might have a high positive correlation because both sectors respond to similar economic conditions. Conversely, bonds and stocks often show negative correlation because when economic uncertainty rises, investors typically flee stocks for the safety of bonds.
Why It Matters for Investors
Correlation is the foundation of diversification. By combining assets with low or negative correlations, you reduce portfolio risk without necessarily sacrificing returns. If all your investments move together, you haven't truly diversified—you've just multiplied your exposure to the same market forces.
For angel investors specifically, correlation becomes critical when managing a portfolio of startup investments alongside traditional assets. Early-stage companies often have low correlation with public markets, meaning they can provide portfolio balance. However, during severe economic downturns, many assets' correlations tend to increase toward +1, reducing diversification benefits when you need them most.
Example
Imagine you invest $500,000 across three assets: a tech startup (venture investment), Treasury bonds, and a real estate fund. Tech startups and Treasury bonds historically show low positive or slightly negative correlation. During an economic slowdown, the startup's valuation might contract (though less predictably than public stocks), while Treasury bonds typically appreciate as investors seek safety. The real estate fund may remain relatively stable. This combination provides better downside protection than investing the full amount in tech startups alone.
Key Takeaways
- Correlation ranges from -1 to +1 and measures how assets move relative to each other
- Low or negative correlations between portfolio holdings reduce overall risk without sacrificing return potential
- Correlations are not static—they tend to increase during market crises when you need diversification most
- True diversification requires selecting assets with meaningfully different correlation characteristics, not just different asset classes