Well calibrated, unevenly priced: what 18,238 settled sports markets say about market forecasts

Well calibrated, unevenly priced What 18,238 settled sports markets say about market forecasts and where the margin sits Edward Glush · Bet Better, Melbourne · 2026 Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 1/9

A price is a forecast Decimal odds of 1.54 imply 1 / 1.54 = 65% once the margin is removed Forecasts can be scored: group by stated chance, count how often it happened This is calibration, the same test used for weather, medicine and ML models Question: how well calibrated is the aggregated fixed-odds market? Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 2/9

Data and method 18,238 settled two-outcome markets, November 2024 to July 2026 Five sports, match-level markets and player-proposition markets Margin removed proportionally; both sides of every market kept 36,476 rows: net 50/50 by construction, no one’s selections inside Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 3/9

Calibration by probability band All markets, both sides of every market included (36,476 observations) Probability band 10 20% 20 30% 30 40% 40 50% 50 60% 60 70% 70 80% 80 90% Observations 2,144 5,263 4,909 5,515 6,077 4,945 5,251 2,157 Mean implied 17.5% 25.2% 34.7% 45.7% 53.8% 65.2% 74.7% 82.5% Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 Realised frequency 18.8% 26.7% 37.0% 46.4% 53.2% 63.0% 73.3% 80.9% Gap (points) +1.4 +1.4 +2.2 +0.7 -0.6 -2.2 -1.4 -1.6 4/9

Reliability diagram Realised frequency against implied probability. Points sit near the diagonal: slightly above it below 50%, slightly b 90 Perfect calibration Observed (all markets) 80 80 90% 70 80% Realised frequency (%) 70 60 70% 60 50 60% 50 40 50% 40 30 40% 30 20 30% 20 10 10 20% 10 20 30 40 50 60 70 Mean implied probability, margin removed (%) Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 80 90 3 2 1 0 1 2 Gap: realised minus implied (points) 5/9 3

Finding 1 · the market is a very good forecas Every band lands within about two points of its implied probability A 65% chance happened about 63% of the time; a 25% chance about 27% A demanding benchmark for any forecasting model Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 6/9

Finding 2 · the residual tilt is systematic Every band below 50% overperforms (+0.7 to +2.2 points) Every band above 50% underperforms ( 0.6 to 2.2 points) Player-proposition markets show roughly twice the tilt of match markets The same markets carry the highest quoted margins (7.93% vs 4.77% two-way) Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 7/9

Interpretation · the margin lives on the longs Margin is not spread evenly: more of it sits on the outsider’s price Proportional de-vigging then leaves exactly this residual signature Caveat: the de-vig method choice affects measured tail behaviour The open data let anyone re-run it under another allocation Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 8/9

Try it yourself Study and teaching data set: betbetter.world/studies/market-calibration Daily margin index, 38 competitions: betbetter.world/studies/margin-index How margins are measured: betbetter.world/studies/bookmaker-margins Free model API, no key, clients in 13 languages: betbetter.world/api/ Everything above is CC BY 4.0 · statistics for education, not betting advice Edward Glush · Bet Better · betbetter.world/studies/market-calibration · CC BY 4.0 9/9