- Residual
- Actual Transfermarkt value minus the model's estimate, on the log scale. Positive means the model under-predicted the player.
- Gap
- Mean residual of non-UEFA players minus that of UEFA players. Positive means non-UEFA players are under-predicted more.
- Within leagues
- Gaps are computed inside each league, then weighted by where non-UEFA players play, so league mix cannot create the gap.
- Held out
- Every residual comes from a model that never saw that player (5-fold cross-validation). Group is never used in training.
- Uncertainty
- 95% intervals from a 2,000-replicate stratified bootstrap of the held-out predictions. They do not include refit variance.
- Groups
- UEFA or non-UEFA by the confederation of a player's first-listed citizenship. Dual nationals are classified by that first entry.
- Model A and Model B
- Model A: Performance, age and position, plus the league and the club's strength. Model B: Performance, age and position only. League and club are left out.