How do we validate that our strategy is not overfitted?
Walk-forward validation: train strategy on rolling window (e.g., 6 months), test on the next month, advance by one month and repeat. Compare in-sample to out-of-sample Sharpe ratio — significant degradation indicates overfitting. Parameter sensitivity analysis: vary each parameter ±20% and measure performance change. Robust strategies are insensitive to small parameter perturbations.