Anfield of dreams: Andy Robertson has moved from being relegated with Hull to a Champions League winner with Liverpool. Photo: Andrew Powell/Liverpool FC via Getty Images

Andrew Robertson was Liverpool's best "overlooked" signing and one reason why the club hired Jurgen Klopp was because they worked out he had been one of the "unluckiest" managers in Europe over a 10-year period.

Ian Graham, Liverpool's director of research, has offered a fascinating insight into his work, including using "missile tracking" technology to assess players, and says Mohamed Salah, who he had urged Klopp to sign, would be worth far more than €150 million if he were sold.

Graham, who runs the data analysis at Liverpool, told the Freakonomics Radio podcast 'Can Britain Get Its 'Great' Back?' "that Robertson, who arrived from relegated Hull City for £8 million in 2017, was his favourite "discovery signing".

He explained: "The sort of players I really like shine through in the data but don't naturally shine through for your typical football fan or even your typical scout.

"He's a sort of awkward, ungainly player or a player who has been overlooked for various other purposes. One of my favourite players is Andy Robertson, who is one of the best left-backs in Europe."

Robertson started playing in the Premier League when he was 20 with a struggling team in Hull.

"Andy Robertson's problem was his background as much as anything," Graham told podcast host Stephen Dubner. "They [Hull] got relegated from the Premier League and he was the best young full-back in Britain at the time.

"He was a really strange case of a really attacking full-back playing in a really poor defensive team."

Graham uses his background - he has a PhD in theoretical physics from Cambridge University - to analyse players.

The Welshman, who grew up a Liverpool fan, created his own model to evaluate players and works out of the club's Melwood training ground with his analytics team. For four years, up until 2012 he had worked for Tottenham Hotspur.

Frames

Graham and his team use data on every touch that every player makes during a game, where they are on the pitch and where it happens and employ "optical tracking", the same technology developed by the military for tracking missiles. The analysts receive "25 frames per second" of where every player is on the pitch.

In the podcast, Graham explained that one of his least favourite measures was a player's "pass completion rate" as he argued that it often distorted in favour of players who only attempted easy passes as opposed to those who played more risky balls which have a greater chance of leading to a goal.

There is therefore an argument that it is very easy to "massage statistics" so that a player can achieve a high pass completion rate without actually helping his team create a goalscoring chance.

"The passes I really love are the passes that go in behind the opposition's defence and take four or five defenders out of the game," Graham explained.

His work is allied to traditional scouting with Liverpool having detailed data on hundreds of thousands of players with his team of analysts helping the "filtering" down of possible targets to be looked at.

Graham does not examine video evidence or scout players himself beyond analysing the data. That process also applies to hiring a manager with Graham playing "a small role" in pursuing Klopp in 2015.

"Our owners and me and all my colleagues were huge fans of Jurgen and his Dortmund team in the early 2010s," he said. "They played the most exciting brand of football in Europe and coming from a place really not of financial dominance. They won the German Bundesliga twice at a huge financial deficit compared to Bayern Munich and so he was always one of our dream hires as manager but his last season at Dortmund was disastrous."

Graham created a mathematical model of every pass, shot and tackle during Klopp's years at Dortmund to evaluate each game and how they should have ended. It showed that, even in Klopp's final season at Dortmund, when they finished seventh, they should have come second. The analysis proved that the results did not match Dortmund's performances.

"So I analysed 10 seasons of Bundesliga performances and Dortmund were the second unluckiest team in that 10-year history. It was just some terrible luck cost Jurgen," Graham said.

In the podcast Graham discussed how Klopp had embraced his work. When it came to signing Salah from Roma for £34 million, Klopp had to be persuaded. Graham was asked how much the 27-year-old would now be worth in the transfer market and said: "He's not for sale. If we could benchmark him against a recent player that we sold which was Philippe Coutinho to Barcelona your minimum starting bid would be €150 million at which point the answer would be 'no, stop wasting our time'." (© Daily Telegraph, London)

Telegraph.co.uk