Even some algo traders don't know how to walk-forward analyze?

Hey everyone, I keep seeing people presenting one single long backtest as proof that their strategy works. That is basically not a test at all, because you use one period to develop (fit) a strategy and then expect it to work on another period. That's called a curve fit. Curve fits don't work on another curve, unless you want to be a gambler. To evaluate whether a strategy actually has an edge, you should perform a walk-forward analysis (WFA). The idea is that the strategy has to repeatedly survive unseen market periods after recalibration. That is much harder than simply fitting one long historical sample. If at least about 10 independent forward out-of-sample cycles remain profitable/stable, then you probably start seeing evidence of real statistical significance, rather than pure historical fitting. Simple example of a rolling WFA: You are currently at month 25. Cycle 1: * Months 13–15: optimization/recalibration in-sample (IS) * Months 10–12: backward out-of-sample (OOS) validation * Months 16–17: forward OOS test Cycle 2: * Months 15–17: optimization IS * Months 12–14: backward OOS validation * Months 18–19: forward OOS test And so on. Much success!