FairValue

Checking model

Esc
  • EnvironmentOverviewWhat FairValue measures, what it found, where to go next.
  • EnvironmentTerminalExplore, compare and track players; market, league and model views.
  • EnvironmentStoriesValuations, head-to-heads and research findings, told as stories.
  • TerminalPlayer ExplorerSearch, filter and sort the player export.
  • TerminalComparison StudioTwo to four players on one scale.
  • TerminalWatchlistsNamed collections, kept in this browser.
  • TerminalMarket LandscapeHow observed value is distributed, and where the model drifts.

↑ ↓ to move · Enter to open · Esc to closeLoading player index…

Portrait of Kieran Tierney

Kieran

Tierney

LBScotland · Celtic FC

№ 300716Established €3.5M +0.84

Image: FootyLogos

Player dossierPremiership

KieranTierney

LBLeft-BackDefender

Club
Celtic FC
League
Premiership
Nationality
Scotland
Age
28
Height
180 cm
Foot
Left
Valued
20 May 2026

Reading the valuation

The market values Tierney at €8M. Model A, which never saw Tierney during training, estimates €3.5M: the market value is 131% above that estimate.

That is a factor of ×2.31. Model A's typical held-out miss is ×1.50 either way, so this gap is larger than its usual error.

Without league and club, Model B estimates €5.7M, closer to the market here, although it is usually further off (typical miss ×2.07).

A gap describes the model's arithmetic for this player's inputs, not what the player is worth.

▲ +0.84A €3.5M▲ +0.34B €5.7M
Pitch length is a log value scale fitted to this player's figures. ● observed · ◇ Model A · dashed ◇ Model B · each arc is a residual, log(observed) − log(estimate).
Apps
63
Minutes
3,617
Goals
6
Assists
8
Started
41/63
Min / app
57
Cards
2Y 0R

Club matches, two years to the valuation date

The Valuation Journey

What moves Model A

Asking the prediction API to explain Model A for Tierney…

SHAP describes the model's arithmetic for this player's inputs, not what causes market value. Model B can be explained only by the live service; Model A also has a published explanation for the research players.

Model A vs Model B against the observed €8M

Checking API
EmergingEstablishedEliteWorld Class€2M€10M€30M€100k€1M€100MMarket €8MModel A €3.5M

Asking the prediction API…

Held-out estimates come from cross-validation, with this player outside the training data: the honest comparison. Served models were refitted on every player, this one included, so they sit closer to the market. Shaded band: Model A's typical miss (×1.50 either way).

Player traitspercentiles vs 2,065 defenders

Kieran Tierney's percentiles among defenders: Goals per 90 95th, Assists per 90 95th, Minutes, two years 64th, Starts 21st, Minutes, last 365 days 93rd, European club minutes 93rd95thGoals95thAssists64thMinutes21stStarts93rdRecent93rdEurope

Dashed ring: the defender median (50th percentile)

Goals per 90

Club goals per 90 minutes played in the two years to the valuation date.

0.15 this player0.03 defender median95th percentile

0.00peer deciles · median line · this player ●0.41

No passing, progression or defensive actions exist in the dataset, so no trait claims to measure them.

Valuation history every Transfermarkt valuation on record

First valuation
€100k
Oct 2015
Peak
€32M
Oct 2020
Model target
€8M
May 2026
Valuations
28
5 club changes
May 2026€8MCeltic FCValuation the model is trained to reproduce

May 2026: €8M, Celtic FC. Dotted lines mark the €2M, €10M and €30M tier boundaries.

Show as a table
DateMarket valueClub
2015-10-14€100kCeltic Glasgow U20
2015-12-28€500kCeltic Glasgow U20
2017-02-14€2MCeltic FC
2018-03-04€5MCeltic FC
2018-08-08€12.5MCeltic FC
2019-01-03€12.5MCeltic FC
2019-09-12€25MArsenal FC
2019-12-10€25MArsenal FC
2020-04-08€20MArsenal FC
2020-07-30€28MArsenal FC
2020-10-13€32MArsenal FC
2020-12-17€28MArsenal FC
2021-03-18€30MArsenal FC
2021-05-28€32MArsenal FC
2021-12-23€32MArsenal FC
2022-06-15€32MArsenal FC
2022-11-03€30MArsenal FC
2023-03-16€25MArsenal FC
2023-06-20€25MArsenal FC
2023-12-22€18MReal Sociedad
2024-03-21€12MReal Sociedad
2024-06-07€12MReal Sociedad
2024-10-01€10MArsenal FC
2024-12-16€10MArsenal FC
2025-05-30€9MArsenal FC
2025-10-08€8MCeltic FC
2025-12-10€8MCeltic FC
2026-05-20€8MCeltic FC

Audit context group-level, not about this player

Audit group
UEFA
Population gap, Model A
+0.093 95% CI +0.063 to +0.124
This player, market vs held-out A
+0.836

The group comes from first-listed citizenship and is never a model input. Across the population, non-UEFA players' market values sit about 10% above Model A's held-out estimates, relative to UEFA players in the same leagues. One player's residual says nothing about that pattern (typical miss ×1.50), and none of it is evidence of discrimination: the target may itself be biased. Open the Fairness Audit

In context observed value among comparable players in this build

All players in the Terminal →

Premiership311 players · median €400k

Joint 10th highest observed value among 311 Premiership players.

€20k€150k€1M€7.5M€8MSee them in the Explorer →

Defenders, all leagues2,065 players · median €2M

Valued above 78% of the 2,065 defenders.

€20k€200k€2M€20M€8MSee them in the Explorer →

Where Tierney appears

Watchlists and the comparison tray are kept in this browser only.

Near this valuation closest observed values: same league, then same position

Counts and ranks of observed Transfermarkt values only; model errors are never ranked here. Full player export: Every player in the modelling population (D-011).