They claim 30 variables plus the following -
- Contract duration
- Year of transfer
- Book value
- Loan status
- Level of buying club (estimated)
Using Sigurdsson as the e.g. as everybody seems to be - he would have been expected to go to a club of similar status to Swansea as he's not a rising star and hasn't had much 'success' nor is he in the 'limelight'. That means his value is automatically judged to be lower than players of similar age but with higher 'status'. You could probably name several players of the same age, same book value who are valued higher because they would be wanted by the bigger clubs. I don't know how Swansea managed to get over the odds for him even in the light of crazy summer prices but I'm confident it wasn't based on book value. Interestingly his price on FF went down when he moved to Everton

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