Why Genetic Algorithms Can Overffit Trading Strategies — and How to Prevent It
Genetic algorithms (GAs) are powerful tools for optimizing trading strategy parameters, but are prone to overfitting when applied naively to backtests. The core risk lies in fitness function misspecification — rewarding raw returns instead of risk-adjusted metrics like Sharpe ratio, consistency across time periods, and drawdown limits. To prevent overfitting, practitioners should use walk-forward testing, evolving parameters on in-sample data and validating on out-of-sample windows the algorithm never trained on. A final held-out data vault, never touched during development, serves as the ultimate check on whether a discovered edge is real or illusory. Additional safeguards include decaying mutation rates, elitism, diversity pressure, and ensuring the backtest and live trading systems share identical code paths.
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