What makes a transfer successful? Is it the number of trophies a team win while a player is there? The number of goals they score? The number of clean sheets? Some ineffable kind of eye-test-driven satisfaction? Or, simply, just how often they play?
Among those options, I'd side with the last one. Club-record transfers play, on average, about only 50% of the available minutes for their new teams. A successful transfer, then, might just be a player who starts more than half of the team's matches. A low bar, sure, but if you spend a lot of money on a player and they play that often, you're actually gaining ground on your rivals.
Of course, that doesn't account for the fee the team paid. And it also ignores the player's age and potential for them to be moved to another team for another fee, which could then be reinvested into the squad.
Earlier this summer -- with the help of NFL analyst Kevin Cole -- I came up with another way of judging transfer success: look at a player's estimated market value a year after they are signed and compare it to the fee the club had to pay. We used this to judge the 100 biggest transfers in the men's game from the previous four seasons, and now we can use it to project the biggest from the window that just closed.
How are the 30 priciest moves of the summer likely to age? Let's rank them, from best to worst.
But first, an explanation of our transfer value rankings
With the piece I wrote in July, we looked at the 25 most expensive transfers in each of the past four seasons. Kevin then ran a basic linear regression to determine which factors seemed to predict a market value higher than the initial transfer fee a year later and how much predictive power each factor had.
Although central midfielders, on average, saw a nearly 10% increase in value after a year, overall we didn't find position to be a statistically significant factor. To varying degrees, a lower age, a lower transfer fee, and a higher market value at the time of the transfer made it more likely there was an increase in value after a year. Then, we can take those factors and create a formula to predict an increase or decrease in value for any big transfer.
In other words: a year from now, is a player's market value likely to be higher or lower than their transfer fee, and by how much?