Ball Retention Percentage vs Transfer Fee
by deg0ey on Sep 7, 2011 1:42 PM BST
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PrintApologies in advance for the rough and ready nature of this post.
In the comments on TPalmer's wonderful Raul Meireles Statistical Breakdown, someone decided that due to the relative ball retention percentages and some other convoluted logic that, even when considering the differences in price, Chelsea should have bid more money for Modric because "his market value if he was put up for sale would be about £60m".
I have taken the liberty of collecting the data on 'ball-retention percentage' (BR%) of a few midfielders transferred this summer and it turns out that there's a pretty good correlation between BR% and transfer fee.
Here's the data that I've found for transfer fees and BR%:
Charlie Adam - £7m - 46.5
Charles N'Zogbia - £9.5m - 44.6
Mikel Arteta - £10m - 70.6
Raul Meireles - £12m - 53.1
Ashley Young - £15m - 49.8
Stewart Downing - £20m - 53.3
Samir Nasri - £25m - 61.0
Cesc Fabregas - £26m - 66.9
These fees are the 'reported' values; some of them will be estimates if the official fee has not been disclosed, but they're the best numbers we have. Anyway, when these are put into a chart, it's easy to see the relationship between the two variables:
It's not the greatest of charts (just knocked it out in Excel), but excluding the obvious outlier, Mikel Arteta (whose transfer fee was lower than his skill would suggest because of his injury history and how desperate Everton are for money) there is a reasonable correlation here between BR% and transfer fee.
It is therefore not unreasonable to conclude that based on Luka Modric's BR% of 62, a reasonable 'market value' would be much closer to £25m than the £60m previously claimed.
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Good stuff
Interesting to see Arteta had a better BR rate than Fabregas. Probably due to the nature of their roles in team’s play though.
Arsenal relied on Fabregas more for through balls than Everton relied on Arteta for the same thing, probably because Everton have wingers that can cross.
As a side note, how did you calculate ball retention?
I used (Completed passes + Shots) as a percentage of the number of times they got the ball. I figured that getting a shot off is the end goal anyway, so they shouldn’t be penalised for that and I couldn’t think of anything other than a completed pass that didn’t involve giving the ball away.
I considered it, but I decided that most shots are in the general vicinity of the goal and it was unfair to penalise people for trying to score. If it was easier to separate those shots that miss by a mile then it’d be easier to figure out. As it is, I don’t think it would make a huge amount of difference overall anyway so I was happy enough just using total shots.
I'm not 100% how to calculate that
But I put my numbers into a formula called ‘RSQ’ in Excel and it gave a value of 0.23. I then used the same formula after removing the details for Arteta and got a much more impressive-sounding 0.84.
That means....
… that 23% of the variance in the data is explained by your variable. 23% is a decent but fairly low correlation, but removing data points isn’t the way to boost it. Instead you’d want to add data points and explanatory variables.
For instance, I know that LFC’s transfers in the summer window wasn’t about maximizing ball retention %, but about increasing chances created. Their transfers in — esp Henderson, Downing, Adam — were all among the league leaders in chances created last year. So, potentially, that stat would have more explanatory power in determining their transfer fees in at least some cases.
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