The study has calculated the estimated worth of footballers and compared it with their actual transfer value.
The CIES estimate the value of the player by looking at his age, playing position, contract situation, international status, experience, performance and the level of competition the individual plays at.
Barcelona overpaid by more than €15 million according to the report.
Turan is unable to play for Barcelona due to a FIFA imposed transfer ban however, the 28-year-old played an hour of football against the Dutch on Sunday. Barcelona will be able to register players once again in January 2016.
The 28-year-old has now scored twice and provided two assists in his last three Euro 2016 Qualifying games for Turkey.
Turkey take on Iceland and the Czech Republic in their next two Euro 2016 qualification games.