The OU chip on the Fear & Greed forecast is an Ornstein–Uhlenbeck process (its discrete-time twin is the AR(1) autoregression) fitted to the index's own history: one equilibrium level, one reversion speed, one noise scale. It is the switcher’s simplest, most honest benchmark — the bar every fancier model must beat.
Fear & Greed is a natural mean-reverting series: panics and melt-ups do not last forever, they decay back toward the middle. The OU model encodes exactly that and nothing more — a reading of 15 (extreme fear) is expected to drift up toward the long-run average, an 85 (extreme greed) to drift down, each at a steady speed. Because it has so few moving parts it is hard to overfit and easy to trust, which is precisely why it earns the role of benchmark.
The OU chip is the bar every fancier model must clear. If a Market Conditions, machine-learning or path-integral model cannot beat this one-line baseline on the walk-forward backtest, its extra complexity is not buying you anything. You can check that yourself: the "Model performance" table under the Fear & Greed forecast re-runs the backtest on current data and reports coverage, MAPE, RMSE, Brier and directional hit-rate for every model side by side — so the ranking is something you verify, not something we ask you to take on faith.
That the Fear & Greed index mean-reverts: a reading that strays from its long-run normal is pulled back toward it, and the further it strays, the stronger the pull. It has just three quantities — an equilibrium level, a reversion speed and a noise scale.
Because it is the simplest model that still captures the one thing sentiment reliably does — normalise from extremes. Every more complex model in the switcher (AR(2), Market Conditions, ML, Q-PI) has to beat it on the walk-forward backtest to justify its extra parameters.
Open the 'Model performance' table under the Fear & Greed forecast chart — it re-runs the walk-forward backtest on current data and shows OU's coverage, MAPE, RMSE, Brier and hit-rate next to every other model, so you can compare them yourself.
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Educational research only — not investment advice.