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Realized correlation measures the actual observed correlation among index components over a historical window. Comparing realized correlation to implied correlation reveals the correlation risk premium, similar to how IV-vs-realized vol shows the variance risk premium.
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Key takeawayRealized correlation is almost always lower than implied correlation, creating a persistent correlation risk premium. This is one reason selling SPX strangles has a structural edge over selling strangles on individual components.
💡 Why It Matters
Realized correlation measures how correlated index components actually moved, providing the benchmark against which implied correlation premium is measured. The persistent gap between implied and realized correlation is one of the most reliable risk premiums in options markets.
⚙ How It Works
Realized correlation is calculated from the actual pairwise return correlations of index components over a historical window. It is typically measured using daily returns over 30, 60, or 90-day windows. During market stress, realized correlation spikes toward 1.0 as all stocks sell off together.
📋 Example
Over the past 60 days, realized correlation among S&P 500 components averaged 0.35, while implied correlation for the same period averaged 0.55. The 0.20 correlation risk premium contributed approximately 2 vol points to SPX IV relative to component-weighted IV. Premium sellers on SPX collected this extra 2 points.
⚠ Common Mistakes
Traders assume realized correlation is stable. During crises, realized correlation can jump from 0.30 to 0.80 within days as the sell-everything trade kicks in. This correlation spike is exactly when index premium sellers face their worst outcomes, as the diversification discount disappears.
❓ FAQ
What is Realized Correlation?
Realized correlation measures the actual observed correlation among index components over a historical window. Comparing realized correlation to implied correlation reveals the correlation risk premium, similar to how IV-vs-realized vol shows the variance risk premium.
Why does Realized Correlation matter for premium sellers?
Realized correlation is almost always lower than implied correlation, creating a persistent correlation risk premium. This is one reason selling SPX strangles has a structural edge over selling strangles on individual components.
How does Realized Correlation work?
Realized correlation is calculated from the actual pairwise return correlations of index components over a historical window. It is typically measured using daily returns over 30, 60, or 90-day windows. During market stress, realized correlation spikes toward 1.0 as all stocks sell off together.
What are common mistakes with Realized Correlation?
Traders assume realized correlation is stable. During crises, realized correlation can jump from 0.30 to 0.80 within days as the sell-everything trade kicks in. This correlation spike is exactly when index premium sellers face their worst outcomes, as the diversification discount disappears.
Related Terms
Close-to-Close Volatility
A basic volatility estimator using only daily closing prices.
Corridor Variance Swap
A corridor variance swap pays realized variance only when the underlying trades within a specified price range (corridor).
CPI Print
The CPI print is the monthly Consumer Price Index release by the Bureau of Labor Statistics, typically at 8:30 AM ET.
Dispersion Trading
Dispersion trading exploits the persistent premium of index implied volatility over the weighted average of its component implied volatilities.
This is not financial advice. Read our full investment disclaimer.