A discriminator, not a predictor.
This is the single most important idea on the site, and the easiest to get wrong. A signal can clearly tell crash-weeks apart from ordinary weeks after the fact, and still be almost useless as a warning. Both things are true at once. Here's why.
Two different questions
Discrimination asks: looking back, did this signal run differently in the days before a crash than on an ordinary day? Several of ours do; that's a real result. Prediction asks something much harder: if the signal fires tomorrow, will a crash actually follow? The gap between the two is created by one stubborn fact: crashes are rare.
What happens when it fires
Take a generous version of our best signal across 1,000 days. It fires on about 687 of them. But because crashes are so rare to begin with, only about 18 of those fires are actually followed by a crash. The other 669 are false alarms.
| days it fires | a crash follows | false alarms | |
|---|---|---|---|
| per 1,000 days | 687 | 18 | 669 |
So even at its best, a fire is followed by a crash about one time in 37, roughly a 2.7% hit rate. The single signal that held up across the whole record (HA07d), at its real numbers. When it fires, a crash follows ~1 time in 37, wrong the other ~36. Every other tested signal sits at a lower or equal lift. This reads the body; it does not predict it. A weather report, not an alarm.
The honest ceiling, as a ladder
Findings are sorted not by how exciting they look but by how far they actually reach:
- Tier A Predictive No signal here reaches this.
Forward-validated: when it fires, a crash reliably follows. Could be called a warning.
- Tier B Informative pattern Where our best findings sit.
Separates crash-weeks from ordinary weeks in hindsight, but a fire does not reliably precede a crash. A description, not a warning.
- Tier C Worth watching The descriptive tier.
A real, describable sign in the body you can keep an eye on, a weather sign, not a forecast (the framework's tier-1 'monitoring').
The real method behind these numbers (posterior-per-fire and the precision tiers) in the research repo: specificity-tables-spec.md ↗