What a chance means
When Vesta gives a team 45%, a team in that position wins about 45 times in 100: not every time, not never. A good model is one whose 45% come true 45% of the time. That is calibration, and it is measured in public, kind by kind, on the track record.
Club matches
- Data. Every match of the Premier League, La Liga, Serie A, Bundesliga and Ligue 1 since 2014-15: results and expected goals, the quality of the chances each team created. Older seasons, back to 2001-02, are on the site but Vesta does not learn from them.
- Strength. Each team's attack and defence, from the chances it creates and allows and from its results, recent matches weighing more, with home advantage and the players a team is likely to field.
- Every score. From the strengths, each side's expected goals and the chance of every exact score. Every other forecast of the match is added up from those scores, so they always agree.
- Calibration. A last step adjusts the chances so that, on past seasons, what Vesta says matches what happens. Only what was known before kick-off is used.
National teams
Every international since 1872, with an Elo rating updated after each match: competitive matches weigh more, and home advantage counts unless the ground is neutral.
Beyond the result
- Players. Each player's chance to start, from the starting-eleven model; his chance to score and to assist, from Vesta's goals for his team, his share of its chances and the minutes he should play.
- Numbers to expect. Shots, shots on target, corners, fouls and cards of each side.
- Season projections. The rest of each league played 10,000 times with Vesta's chances.
How every kind is checked
Two checks, never mixed. The published forecasts: the last one before kick-off of each match, kept as it was, checked after the final whistle. The past seasons: each season hidden from Vesta and predicted with a model fitted only on the seasons before it, so it never sees the matches it is judged on.
For each kind of forecast (each result, each goal line, each score, each player chance, each number) the track record shows what Vesta said and what happened, grouped by the size of the chance. Beside the forecasts of a match, each chance shows how chances of the same size and kind have done.
What Vesta cannot know
News after the forecast was made, like an injury or a surprise line-up; weather, travel, motivation. That is why a 70% favourite still fails to win three times in ten. No tips and no odds: the numbers are for information.