Founder of Bet Better, a Melbourne sports-analytics company. I talk about forecast calibration, bookmaker margins and open sports data.
A price is a forecast, and forecasts can be scored. This deck walks through a calibration check of margin-free sports prices on both sides of 18,238 settled two-outcome markets (36,476 observations, five sports, November 2024 to July 2026). The market turns out to be a very good forecaster: every probability band lands within about two points of its stated chance. The small residual tilt is systematic, with outsiders overperforming and favourites underperforming, and is roughly twice as large in player-proposition markets, the same markets that carry the highest quoted margins. The reading is that the margin is loaded onto the longshot side.
The study, its teaching data set and the figures are open under CC BY 4.0: market calibration study, daily bookmaker margin index, how margins are measured and the free model API with no key. Statistics for education and analysis, not betting advice.