How Efficient Are Prediction Markets? A Calibration Study of 9.5 Million Trades

Across 9.46 million resolved Polymarket positions, implied prices track real outcomes closely: a 5-cent contract resolves true 3.5% of the time, a 95-cent contract 98.4%. The gap opens in the middle, where positions priced 45 to 65 cents win 6 to 9 points more often than the price implied. Here is the calibration curve, the method behind it, and how the per-trader edge is distributed across 8,705…