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…

Mathieu

Maertens

AMBelgium · Oud-Heverlee Leuven

№ 310131Emerging €650k −0.08

Player dossierPro League

MathieuMaertens

AMAttacking MidfieldMidfield

Club
Oud-Heverlee Leuven
League
Pro League
Nationality
Belgium
Age
31
Height
185 cm
Foot
Right
Valued
4 Jun 2026

Reading the valuation

The market values Maertens at €600k. Model A, which never saw Maertens during training, estimates €650k: the market value is 8% below that estimate.

That is a factor of ×1.08. Model A's typical held-out miss is ×1.50 either way, so this gap is within its usual error.

Without league and club, Model B estimates €685k, further from the market. Model B is usually further off (typical miss ×2.07): league and club explain much of how the market prices players.

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

▼ −0.08A €650k▼ −0.13B €685k
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
47
Minutes
2,051
Goals
2
Assists
4
Started
23/47
Min / app
44
Cards
6Y 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 Maertens…

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 €600k

Checking API
EmergingEstablishedEliteWorld Class€2M€10M€30M€100k€1M€100MMarket €600kModel A €650k

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 1,687 midfielders

Mathieu Maertens's percentiles among midfielders: Goals per 90 51st, Assists per 90 77th, Minutes, two years 38th, Starts 20th, Minutes, last 365 days 40th, European club minutes 30th51stGoals77thAssists38thMinutes20thStarts40thRecent30thEurope

Dashed ring: the midfielder median (50th percentile)

Assists per 90

Club assists per 90 minutes in the same window.

0.18 this player0.09 midfielder median77th percentile

0.00peer deciles · median line · this player ●0.74

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 2014
Peak
€3M
Nov 2022
Model target
€600k
Jun 2026
Valuations
31
1 club change
Jun 2026€600kOud-Heverlee LeuvenValuation the model is trained to reproduce

Jun 2026: €600k, Oud-Heverlee Leuven. Dotted lines mark the €2M, €10M and €30M tier boundaries.

Show as a table
DateMarket valueClub
2014-10-05€100kCercle Brugge
2015-03-24€200kCercle Brugge
2015-06-24€300kCercle Brugge
2015-10-28€450kCercle Brugge
2016-02-04€500kCercle Brugge
2016-08-03€600kCercle Brugge
2017-01-21€500kCercle Brugge
2017-06-06€500kCercle Brugge
2017-10-25€600kOud-Heverlee Leuven
2018-04-05€750kOud-Heverlee Leuven
2018-09-14€650kOud-Heverlee Leuven
2019-01-18€600kOud-Heverlee Leuven
2019-06-10€600kOud-Heverlee Leuven
2019-11-13€750kOud-Heverlee Leuven
2020-03-30€900kOud-Heverlee Leuven
2020-04-08€725kOud-Heverlee Leuven
2020-10-16€1MOud-Heverlee Leuven
2021-06-07€1MOud-Heverlee Leuven
2022-01-06€1.3MOud-Heverlee Leuven
2022-04-12€1.5MOud-Heverlee Leuven
2022-09-07€2MOud-Heverlee Leuven
2022-11-04€3MOud-Heverlee Leuven
2023-06-09€2.5MOud-Heverlee Leuven
2023-12-19€2MOud-Heverlee Leuven
2024-06-04€1.8MOud-Heverlee Leuven
2024-10-02€2.3MOud-Heverlee Leuven
2024-12-11€2.2MOud-Heverlee Leuven
2025-06-12€1.8MOud-Heverlee Leuven
2025-10-01€1.2MOud-Heverlee Leuven
2025-12-10€900kOud-Heverlee Leuven
2026-06-04€600kOud-Heverlee Leuven

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
−0.080

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 →

Pro League350 players · median €1.8M

Valued above 13% of the 350 Pro League players.

€100k€750k€5M€30M€600kSee them in the Explorer →

Midfielders, all leagues1,687 players · median €2M

Valued above 20% of the 1,687 midfielders.

€20k€200k€2M€20M€600kSee them in the Explorer →

Where Maertens 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).