Sell index volatility and buy single-stock volatility to profit from the 'correlation risk premium.' The index option is cheaper to hedge than the sum of its parts because of implied correlation overpricing.
History
Dispersion trading emerged from options market-making desks in the late 1990s. The strategy exploits a well-documented phenomenon: index implied volatility tends to overstate the realized volatility of the index relative to its components, because implied correlation is persistently higher than realized correlation. This 'correlation risk premium' exists because investors systematically overpay for index protection (portfolio hedging via index puts). Driessen, Maenhout, and Vilkov (2009) formalized the academic case. Hedge funds like Capstone and Citadel have been prominent practitioners.
How It Works
Sell options (straddles or strangles) on an equity index like the S&P 500
Simultaneously buy options on individual constituent stocks, weighted by their index weight
The net position is short implied correlation: you profit when stocks move independently (low correlation) and lose when they move together (high correlation)
The trade captures the 'correlation risk premium' since implied correlation consistently exceeds realized correlation
Hedge delta exposure on both the index and single-stock legs; the remaining risk is pure correlation exposure
Size legs carefully: the gamma profile of single-stock options differs from index options
Example Trades
SPX implied correlation at 0.65; trailing 30-day realized correlation at 0.42. Premium of 23 correlation points
entry Sell SPX 1-month straddle, buy straddles on top 20 S&P components weighted by index weight
exit Hold to expiry; realized correlation comes in at 0.45
result +20 correlation points of premium captured; ~3.5% return on notional
Related Charts
Who Runs This
When It Works vs. Fails
works
Calm markets with low correlation. Earnings season (individual stocks move on idiosyncratic news, reducing correlation). Normal dispersion between sectors.
fails
Systemic crises where correlation spikes to 1 (all stocks crash together). Macro-driven markets dominated by a single theme (e.g., rate hikes, tariff wars).
Risks
01 Correlation spikes during crises (2008, 2020): when all stocks crash together, the short-index-vol leg suffers massive losses
02 Execution complexity: managing gamma and delta across dozens of single-stock option legs is operationally intensive
03 Liquidity risk: single-stock options can become illiquid in stressed markets, making it hard to exit
04 The premium can compress when too many funds trade dispersion, reducing profitability
Research
Is Default Risk Negatively Related to Stock Returns?
Driessen, Maenhout, Vilkov, 2009
The Price of Correlation Risk
Buss, Vilkov, 2012
Correlation Risk and the Cross-Section of Option Returns
Buraschi, Kosowski, Trojani, 2022