01 / ACCURACY
Brier score
(predicted probability − outcome)²
The squared distance between the forecast and reality. A perfect prediction scores zero.
A OnePercentBetter project
The Closing Line. — a OnePercentBetter project
Grading the closing lines of the world's prediction markets.
01 / What it is
A spectator’s scoreboard for the markets that predict the world.
Which prediction market is sharper? We freeze their probabilities before an event resolves, then grade them against what actually happens. Category by category. Season by season.
The same outcome. Two sets of odds. A score neither venue gets to rewrite.
02 / How scoring works
Use probabilities from 0 to 1. The outcome is 1 if the priced subject wins, and 0 otherwise. Lower scores are better.
02 / CONFIDENCE
Log loss
−ln(probability assigned to the actual outcome)
Punishes confident wrong calls much harder. Being nearly certain and wrong carries a steep cost.
03 / RELIABILITY
Calibration
Stated probability ↔ hit rate
Do 70% calls win about 70% of the time? After results, 10-point probability bins will compare forecasts with hit rates and sample counts.
03 / The seasons
SEASON 01 / POLITICSAwaiting results
Season 1 · 2026 Midterms
Polymarket vs Kalshi. Fourteen Senate races, one control test, and the probabilities frozen before the verdict.
Open the showdown