Correlation is a statistical measure of how two assets move in relation to each other, expressed as a coefficient between -1 and +1. Understanding correlation is essential for building diversified portfolios, managing risk, and implementing strategies like pairs trading. When assets are highly correlated, they don’t provide diversification benefits—they just multiply your exposure.
- Correlation of +1: Assets move perfectly together (no diversification)
- Correlation of 0: No relationship (good for diversification)
- Correlation of -1: Assets move in opposite directions (hedging potential)
How Correlation Works
Correlation quantifies the relationship between two assets’ returns. It tells you what to expect from one asset when the other moves.
Correlation Coefficient (r):
- r = +1.0: Perfect positive correlation
- r = +0.5: Moderate positive correlation
- r = 0: No correlation
- r = -0.5: Moderate negative correlation
- r = -1.0: Perfect negative correlation
The formula uses covariance of returns divided by the product of standard deviations, but most platforms calculate this automatically.
Quick Reference: Correlation Interpretation
| Correlation | Interpretation | Diversification Value |
|---|---|---|
| +0.9 to +1.0 | Very high positive | None—moves together |
| +0.5 to +0.9 | Moderate positive | Limited benefit |
| +0.2 to +0.5 | Low positive | Some benefit |
| -0.2 to +0.2 | Near zero | Strong benefit |
| -0.5 to -0.2 | Low negative | Very strong benefit |
| -1.0 to -0.5 | Moderate/high negative | Hedging potential |
Example: Portfolio Correlation Analysis
Two Portfolios, Same Stocks, Different Correlations:
| Portfolio A: High Correlation | Correlation |
|---|---|
| AAPL & MSFT | 0.82 |
| GOOGL & META | 0.79 |
| NVDA & AMD | 0.88 |
| Average Portfolio Correlation | 0.83 |
| Portfolio B: Low Correlation | Correlation |
|---|---|
| AAPL & XOM | 0.15 |
| JNJ & AMZN | 0.22 |
| GLD & SPY | -0.08 |
| Average Portfolio Correlation | 0.10 |
Result in 20% Market Crash:
- Portfolio A drops ~19% (high correlation = falls together)
- Portfolio B drops ~8% (low correlation = cushions the fall)
Correlation measures how assets move together on a scale from minus one to plus one. Low or negative correlation provides diversification benefits. High correlation means positions move together, multiplying risk rather than spreading it.
Common Asset Correlations
| Asset Pair | Typical Correlation | Notes |
|---|---|---|
| Tech Stocks (FAANG) | +0.7 to +0.9 | Move together in sector trends |
| Stocks & Bonds | +0.2 to -0.3 | Varies by market regime |
| Gold & Stocks | -0.1 to -0.4 | Negative in crises |
| Oil & Energy Stocks | +0.6 to +0.8 | Logically connected |
| USD & Gold | -0.3 to -0.5 | Generally inverse |
Why Correlation Matters
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True diversification – Without understanding correlation, you might think you’re diversified when you’re not. Ten tech stocks don’t diversify risk.
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Risk management – Highly correlated positions multiply your exposure. If everything drops together, your losses compound.
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Pairs trading – Correlation is the foundation of statistical arbitrage strategies that profit from temporary divergences.
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Portfolio construction – Optimal portfolios combine assets with low correlation to maximize returns per unit of risk.
Correlation Breakdown in Crises
A critical concept: correlations tend to spike toward +1 during market panics. Assets that normally move independently suddenly all fall together as investors sell everything.
Example: 2008 and 2020 Crashes
- Normal times: Stocks, commodities, REITs have correlations around 0.3-0.5
- During crashes: Correlations spiked to 0.8-0.95
This means diversification works best in normal markets but provides less protection in extreme events. True crisis hedges require assets with negative correlation in stress (like Treasury bonds or VIX products).
Common Mistakes
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Using short-term correlation – Monthly correlation can be noisy. Use 1-3 year rolling correlation for stable estimates.
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Ignoring regime changes – Correlations shift with market regimes. What was uncorrelated in a bull market may become correlated in a bear market.
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Assuming stability – Historical correlation doesn’t guarantee future correlation. Monitor and adjust regularly.
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Sector confusion – Assuming different stocks means diversification. Five bank stocks are one correlated bet on financials.
How JournalPlus Tracks Correlation
JournalPlus calculates the correlation between your positions to measure true portfolio diversification. You can identify hidden concentration risk, see how correlations change over time, and understand whether your portfolio would survive a correlation-spike event.
