The question is whether Davies is that sort of impact player. In order to answer that question, Pro Soccer USA contacted the German stats company Goalimpact, which uses an algorithm to measure the impact individual players have on the field.
The system is described as follows on the companies homepage: “Starting at approximately two seasons of data input into our system, we can evaluate the current and forecast reliably the player’s future real strength. This is what we call the Goalimpact.”
The database in short measures the extent that a player contributes to the goal difference of a team. A player with a high goal index rating contributes significantly to a positive goal difference when he is on the pitch compared to when he is not on the field.
“We average the impact of all games of a player’s career for all clubs, competitions and seasons in relation to all other players in our database. This rating is adjusted by teammate’s values and the opposition strength and by such factors as the number of minutes played, home advantage, fatigue degree and red cards in a game.”
The best players in the world achieve above 200 index points. Also, every club and league has an average value. The average for the first German Bundesliga, for example, is approx. 119 points with peaks of up to 162 on average for top teams. Spanish La Liga has an average of 111 points and Italian Serie A is rated with a Goalimpact score of 104 on average.
In Biermann’s book “Matchplan,” the company’s founder Jörg Seidel compares his statistics to those of a handicap in golf or the Elo rating system in chess. To put it in Biermann’s words: “Seidel doesn’t suggest that Thomas Müller is a better player than Karim Benzema when the former scores 195 and the later 190. He only suggests that the former is a more valuable player for his team than the later.”
To make the system work, Goalimpact has put together a database that includes 320,000 players from over 200 leagues. Goalimpact includes datasets from leagues from all over the world including many youth competitions.
The system also takes into account age. A 21-year-old player, for example, is calculated to play, on average, worse than a 26-year-old, an age when many players reach their peak. Even a relative age effect is included in which youth players born in the second half of the year are given a handicap in the database – players born in the second half of the year often struggle in youth teams as they play against older players.
When Biermann wrote his book, Seidel pointed out that Alphonso Davies was the highest ranked player in the system with numbers that ranked him alongside Cristiano Ronaldo.