5 · Sensitivity
Is your edge a broad plateau or a knife-edge? Robust systems degrade gracefully.
On the roadmap — not shipped yet
Optimization hands you a best parameter set. Sensitivity analysis asks the more important question: what happens to performance when you're slightly wrong about those parameters? A trustworthy system sits on a broad plateau — nudging a knob barely moves the result. A fragile one sits on a spike — the "best" setting is a statistical accident and its neighbours are losers.
Plateau, not peak
Prefer the middle of a plateau over the tip of a peak
A slightly lower backtest score in a wide flat region beats a slightly higher score on a lonely spike. The plateau will still be there next year; the spike won't.
The reason is simple: your parameters are estimates, and markets drift. If moving
entry_z from 1.25 to 1.4 collapses the return, then the real world — which never
hands you exactly 1.25 — will collapse it for you.
How to test it
One-at-a-time sweeps
Hold everything fixed, vary one parameter across its range, and plot the objective. You want a smooth, flat-topped curve — not a single tall bar.
Neighbourhood check
Around the chosen point, perturb each parameter by ±10–20% and confirm performance stays acceptable. If several small perturbations combine to wreck it, that's a red flag.
Heatmaps for interactions
For two interacting knobs, a 2-D heatmap of the objective reveals whether the good region is a connected plateau or scattered islands (islands = luck).
Relationship to the other stages
Sensitivity is the natural companion to Optimization: the optimizer finds candidates, sensitivity tells you whether a candidate is a real region or a mirage. It differs from Robustness, which perturbs the world (costs, data, regimes) rather than your parameters.
In Malgot
Practise it today, manually: run a small series of Quick Sims varying a single parameter in even steps, and record the objective for each. Even five points reveal whether you're on a plateau or a cliff. The histogram view on each run helps you confirm the shape of returns is stable across the sweep, not just the average.
