‘Moneyball’ is just a media buzzword and what Liverpool actually appear to be using to evaluate potential transfers is an algorithm known as ‘Goalimpact’, which was created around 2004 by a German physicist. It statistically measures the extent to which a player has contributed to the goal difference per minute of his team.
The basic stats that Match of the Day, Sky and WhoScored focus upon - such as tackles, completed passes, goals and assists – play no part in the formula. They have little value as they are so subjective; why should a player be penalised if a teammate fails to control an excellent pass or misses a sitter laid on a plate? Instead, Goalimpact (“GI”) employs a mathematical equation to evaluate how much more likely a team is to win if an individual is selected in the team (and the impact that player will have upon the club’s points total at the end of the season if he plays every game). Players with a current GI rating of around 110 are Premier League quality, 130 is Champions League level and 170+ is elite.
Basically, Goalimpact ascribes a numeric value to reflect the ‘influence’ that a specific player has on the goals scored and conceded by his team while he is on the pitch. It also predicts what his peak GI Rating will be at age 26. The more games played by a player during their career, the more accurate the GI rating.
Wijnaldum is a perfect illustration of the model in action. I could not fathom why the club pursued him out of all the options available until I learned he was ranked 17th in the world on the GI index in April 2015 (182). Liverpool fans endlessly debate what exactly he brings to the table but there is pretty much universal agreement he offers more than Emre Can and the team performs significantly better with him in it.
GI does not explain precisely why a team is more or less successful whenever a particular player is included but does objectively determine the extent to which the team’s performance is affected. It therefore provides a much better insight into actions which are difficult to quantify like positioning, marking, tracking, and creation of space than traditional ‘on the ball’ statistics. Our best performers this season on a GI basis have been Mane, Henderson, Wijnaldum and Lallana. The fact that two are new signings is probably no coincidence.
FSG infamously favour a statistical approach to player trading and it is little wonder they like GI as a metric. The creator, Jorg Seidel, recently selected groups of young players using his algorithm and benchmarked their increases in value against the Transfermarkt website to show its predictive capabilities. The returns on investment ranged from 67% to 145%; this is the prism through which investors like FSG determine value. It allows them to clinically evaluate whether a player has conformed to expectations and added to the performance of the team.
Until I stumbled across GI I could not work out the common thread between our recent transfer targets; Konoplyanka (c. 138 when we were linked), Gotze (200), Draxler (), Dembele, Teixeira, Brandt. Their backgrounds and career achievements are so disparate that it seemed impossible to draw any comparison. However, they all have excellent GI rankings. In fact, Brandt and Gotze’s ratings are staggeringly high and it is therefore little wonder they attracted our attention. Sadio Mane’s GI rank is 177 and that is the territory Brandt is currently projected to reach.
Goalimpact is by no means a secret in the football world and goes a long way towards explaining why our targets so often mirror Dortmund and Spurs; similar tools are being used to inform decisions on transfers at various clubs around Europe. Wolfsburg, Southampton and the Red Bull clubs have used this approach to excellent effect.
Don’t be surprised to see us linked to Martin Hinteregger (Augsburg @ 190), Ilsanker (178), Werner, Keita, Sabitzer (Red Bull Leipzig), Kolasinac (Schalke) or Brandt (Leverkusen @ 142 presently) this Summer. The full GI Index is a closely guarded secret but the Hamburg-based company that produces it periodically releases limited information through Twitter and its website. I have no doubt that the GI Index rankings from 20 – 300 would provide a very clear picture of our targets over coming transfer windows if you focused on players under 26.
TL;DR Goalimpact is how we scout players. If a player linked to us does not have a GI rating of 120+ we probably are not buying him – certainly not for any serious money. We need an average GI in excess of 135 to have a good shout of Champions’ League qualification.