Strategy
Brier score
A measure of forecast accuracy: the average squared difference between predicted probabilities and actual outcomes, where lower is better.
A forecast of 70 percent for an event that happens scores (1 - 0.7)² = 0.09; if it does not happen, (0 - 0.7)² = 0.49. A perpetual 50 percent forecaster scores 0.25. Good prediction markets score around 0.1 to 0.15 a day before resolution on broad sets of questions.
The Brier score rewards calibration (70 percent events happening 70 percent of the time) and resolution (being confident when it counts). It punishes confident misses heavily.
BetG8's scorecard reports a monthly Brier score for the highest-volume resolved markets, using the price one day before close.
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Frequently asked questions
- What does "Brier score" mean?
- A measure of forecast accuracy: the average squared difference between predicted probabilities and actual outcomes, where lower is better.
- Why does brier score matter for prediction markets?
- BetG8's scorecard reports a monthly Brier score for the highest-volume resolved markets, using the price one day before close.