Liverpool number one Alisson is the best performing goalkeeper in the Premier League according to a metric from Stats Perform.
Looking at clean sheets, goals conceded and save percentages only provides a limited analysis of a keeper's performances, as the metrics can be biased by team and defensive strengths.
The expected goals on target (xGOT) model moved things forward and provided a comparison to the performance of an 'average' keeper, but with each of them facing different shots it was difficult to compare the values.
By taking goals conceded away from the xGOT, Vicente Guaita is the best-performing keeper, preventing 6.6 goals (an xGOT of 29.6 minus the 23 goals he has conceded, excluding own goals), while Alisson has a differential of just 0.3 (an xGOT of 6.3 minus the six goals conceded).
The Stats Perform Goalkeeper Index, however, builds on the xGOT model, personalising the estimates to each keeper and simulating how they would perform over the exact same sample of shots.
On top of the start and end location of shots, the index considers a keeper's historic ability to make saves based on factors including shot destination (left, middle or right of the goal) and the angle to the shot trajectory (straight at them, to the left or to the right).
Premier League keepers have faced 2,108 shots this season and the Goalkeeper Index simulates how many goals every number one would have conceded against that set.
When looked at on a game-by-game basis, as well as in comparison to the league average, the impact becomes clear.
At the top of the Goalkeeper Index is Alisson, who is expected to prevent 0.58 more goals per game than the league average – putting him comfortably clear of Manchester City counterpart Ederson (0.27) in the rankings.
Tottenham captain Hugo Lloris' back-up Paulo Gazzaniga (0.16), Manchester United's David de Gea (0.16) and Bernd Leno (0.13) of Arsenal round out the top five.
At the other end of the scale for keepers to play in at least 10 games, Southampton keeper Angus Gunn is expected to concede 0.50 more goals per game than the league average.
Alisson would therefore be expected to prevent 1.08 more goals per game than Gunn.
The Brazil international has conceded one goal every 214 minutes in the Premier League this season. If he maintains his form, he could break Petr Cech's record for minutes per goal conceded by a keeper in the Premier League (242).