Sports prediction strategies: measure forecasts without fooling yourself
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A convincing explanation after a match is not evidence of a useful prediction before it. The simplest improvement is to record the forecast, its probability and the information available at the time, then assess it without rewriting the past.
Write the forecast before the outcome
For each event, record an unambiguous outcome, a probability, a timestamp and a short explanation. Preserve losing forecasts as carefully as winning ones. Separate a model’s forecast from a human override so that you can see which process is being evaluated.
Include a baseline, such as a documented market-implied probability or a simple historical rule. Be careful with bookmaker probabilities: reciprocal decimal odds include margin when summed across mutually exclusive outcomes. Removing that margin requires assumptions; it does not reveal a uniquely correct probability.
Measure calibration, not just winners
If you repeatedly forecast an outcome at 70%, a sufficiently large comparable group should win roughly seven times in ten for that probability to be well calibrated. Small samples vary widely. Do not declare a model accurate from a short winning run.
For binary outcomes, one simple score is the mean of (p - y) squared, where p is the predicted probability and y is 1 for an occurrence and 0 otherwise. A 0.70 forecast scores 0.09 when the event occurs and 0.49 when it does not. Lower is better, but compare results on the same events and preserve uncertainty about small samples.
Keep forecasting and profitability separate
A sensible probability can still be a poor purchase at an unfavourable price. Fees, changing pool participation, execution timing and selection bias all affect realised returns. In a pool market, the displayed estimate can move before close; a journal should record both what you saw and what ultimately settled.
Read the market mechanism rather than assuming every product behaves like a fixed-odds bookmaker.
Use limits that do not depend on confidence
Set an affordable maximum loss and stop when it is reached. A larger stake does not repair an inaccurate forecast. Exclude information published after your recorded decision from backtests, avoid tuning against the final evaluation sample and report every result. These habits improve honesty; they do not guarantee an edge or make gambling an income plan.
Questions
Does a high win rate prove profitability?
No. Prices, stakes, fees and losses determine returns; win rate alone is insufficient.
What should a prediction journal retain?
The timestamped outcome definition, forecast probability, available information, accepted terms and eventual result, including losses.