The British statistician George Box famously wrote, "All models are wrong, but some are useful." No model can be perfect -- reality is too unpredictable and impossible to model -- but the best ones reveal more about how the world works than we knew before.
And so welcome to ESPN's not-exactly-right-but-useful new model: The USMNT Player Performance Index.
We wanted to come up with a way to track the progress of all of the top-level U.S. men's national team players and rank them against one another over the course of the season. But how do you compare, say Timothy Weah fighting for playing time on Juventus with Haji Wright getting tons of minutes for Coventry City? How do you rate the performance of Matt Turner, a goalkeeper, against Christian Pulisic, a winger? What's more valuable: coming off the bench for PSV Eindhoven or playing every minute for the Columbus Crew?
Figuring that out is part of the fun. These rankings are not meant to provide definitive evidence of the best American soccer player, but rather to give a bird's-eye view of who is actually having an impact at the highest levels of the sport. In other words: Who is in form, and who isn't?
Because individual statistics still miss so much of the context for player performance in soccer, we've instead opted for a top-down approach. To create the rankings, we've used three inputs: How much does a player play? How good is the team he plays for? And how does the team perform when he's on the field, compared to off it?
The first part is simple: the percentage of available minutes played. If a USMNT player is trusted to start and play significant minutes for his team, there's a strong likelihood it's because he's doing things that help his team. And if he's not playing, he's not providing any value, no matter how talented he might be.
The second output comes from Opta's power ratings, which rank every club team in the world by a combination of their results, underlying performance and strength of opponent. Each team's rating gets adjusted after every match -- and the more a player plays, the more he contributes to that rating.
The third part of the rankings looks at the team's goal differential per 90 minutes when the player is on the field compared to when he's off it. Is his team better or worse when he's on the field?
Team strength is the biggest component of the rankings (maximum value of 500 points), then playing time (max of 100 points), and then there's a final minor adjustment for the on-off numbers (max adjustment of 10 points, in either direction). This is the first edition, and the formula might vary as the club season wears on.
Notable USMNT absences
A subjective list of the best players on the USMNT would look different, but our goal here is to provide an objective ranking of player form since the start of the current club season. That means some very good players have not landed in the top 50.
In another year, Tyler Adams would be here, and possibly topping the table, but since we're attempting to look at this season, his zero minutes played mean he's not on the list. Daryl Dike, too might've otherwise appeared somewhere on here, but he has played only 52 minutes this season for West Bromwich Albion after tearing his left Achilles just five games after returning from tearing his right Achilles.
Josh Sargent, meanwhile, misses out because he has played only 30% of the minutes for the seventh-place team in England's second division. More consistent playing time, though, and we'll see him on the next edition of this ranking.
Major League Soccer, too, poses a bit of difficulty for the first edition of these rankings. It's too early in the season to have much confidence in team quality or to put too much weight onto how many minutes anyone has played. So, for now, we've used numbers from last season and player values from Transfermarkt to end up with six MLS players in our ranking. For the next edition, we'll have a better baseline for how MLS and their teams are playing this season, which will allow more or different MLS players to break into the list.
With that out of the way, let's dig into our ranking of the top 50 players right now, according to our USMNT Player Performance Index:
