How do correlation trading strategies work, and why is implied correlation often higher than realized correlation?

Correlation trading involves taking positions that profit from changes in the co-movement between assets. While related to dispersion trading, correlation can also be traded more directly through correlation swaps, basket options, and structured products.\n\nImplied vs Realized Correlation:\n\nImplied correlation is extracted from index and component option prices:\n\nrho_implied = (sigma_index^2 - Sum(w_i^2 x sigma_i^2)) / (Sum_i_!=_j(w_i x w_j x sigma_i x sigma_j))\n\nHistorically, implied correlation exceeds realized correlation by 5-15 points because of the correlation risk premium --- investors pay to hedge against the scenario where all assets fall together.\n\nDirect Correlation Instruments:\n\n| Instrument | Mechanism | Liquidity |\n|---|---|---|\n| Correlation swap | Pays realized minus fixed correlation at maturity | OTC, moderate |\n| Dispersion trade | Synthetic correlation short via options | Listed options |\n| Worst-of options | Embedded long correlation (issuer short) | Structured products |\n| Basket variance swap | Captures both vol and correlation | OTC |\n\n`mermaid\ngraph LR\n A[\"Correlation Swap
Strike: 0.55\"] --> B{\"At Maturity\"}\n B -->|\"Realized Corr = 0.40\"| C[\"Buyer pays seller
(0.55 - 0.40) x Notional
= 0.15 x $10M = $1.5M\"]\n B -->|\"Realized Corr = 0.72\"| D[\"Seller pays buyer
(0.72 - 0.55) x Notional
= 0.17 x $10M = $1.7M\"]\n`\n\nWorked Example:\n\nCrestline Capital enters a 6-month correlation swap on the top 5 stocks in the Northfield 100 Index:\n- Strike (fixed) correlation: 0.55\n- Notional: $10M\n- Position: short correlation (pays if realized < strike)\n\nOver 6 months, the average pairwise realized correlation is 0.38.\n\nPayoff = (0.55 - 0.38) x $10M = +$1,700,000\n\nWhy Implied Correlation Is Typically Elevated:\n1. Hedging demand: Portfolio managers buy index puts, pushing up index IV and implied correlation\n2. Crash premium: During crises, stocks become highly correlated (\"correlations go to 1 in a crisis\"), and investors pay for this crash protection\n3. Structured product issuance: Banks sell worst-of products that embed short correlation, hedging by buying correlation in the interdealer market\n\nPortfolio Management Applications:\n- Hedge against correlation spikes during systemic events\n- Express views on macro regime changes (risk-on vs risk-off)\n- Enhance yield through selling the correlation risk premium in calm markets\n\nRisk Warning:\nCorrelation trades have extreme negative skew when you are short correlation. The 2008 financial crisis saw realized correlations surge to 0.85+, causing enormous losses for short correlation books.\n\nPractice correlation analysis in our CFA Derivatives question bank.