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Monday, 22 February 2016

How Roberto Martinez Could Have Been Everton's Most Irreplaceable Player.

Midtjylland's boffin driven win over Manchester United last week along with Rasmus Ankersen peerlessly owning BT's Jake Humphrey in the post match interviews has inevitably put football analytics back in the media spotlight.

Intelligently written prose combined with rigorously derived statistics has a relatively sparse, but nonetheless impressive history in the mainstream British media.

The Guardian's Sean Ingle regularly delivers well written narrative, backed up with accessible use of numbers, often with a slice of contemporary culture thrown in and Daniel Finkelstein's eponymous Fink Tank has long provided an outlet for some of football's best, lab coated number crunchers.

Nerdy clich├ęs aside, it's encouraging to see analytics becoming an accepted part of football reporting. It may not appeal to every taste, but it certainly doesn't seek to wholly replace more subjective approaches. It has only ever mostly been intended to complement and enhance.

But just as analytics has had to learn to walk before it could break into its current brisk canter, some of the emerging mainstream efforts fall well short of the bar set by The Times and The Guardian.

Analytics occasionally over turns "established" knowledge. But this mostly occurs when simple common sense could have eyeballed the flaws in the narrative anyway.

2-0 is a "dangerous" lead that few would turn down given the choice and it's rare to hear a fan base inwardly groan when an opponent is reduced to ten men and they instantly become "harder" to play against.

So analytics does have a record of going against the grain of irrational popular sentiment. But this should not mean that the more outlandish the numbers driven claim, the more likely it is to be true.

Saturday's article in the Telegraph, "The Player Your Premier League Team Cannot Do Without" caught the eye on Twitter, as well as being shared over 2k times.

The premise was simple, the unnamed journalist found the player in each Premier League team, subject to six or more appearances who was that side's "winning-est" player. In plain English, the player(s) who had the best win% in matches they had taken part in at each Premier League club.

The list contained a motley crew of rarely used fringe players mixed with the occasional legitimate star.

Typifying the former and with all due respect was Everton's Leon Osman, although Vardy and Mahrez will no doubt be surprised to learn that Nathan Dyer is the player that Leicester can ill afford to lose this season.

34 year old Osman's six appearances has yielded four wins for a winning-est percentage of 67% compared to Everton's baseline figure of 31% in the Premier League this season.

Player contribution to team success is a well trodden and problematic path in sports analytics, more so in football where the individual, repetitive elements present in other sports, such as baseball and basketball are partly absent.

Nevertheless, the likes of Jorg Seidel and Dan Altman have produce measures that aim to untangle individual player contribution to team success. Neither, I would hazard would consider Osman indispensable to Everton's cause.

We could pick holes in the Telegraph's approach by pointing out that wins, especially over a small number of games in a low scoring sport is a very blunt measuring tool. We've already discarded draws, for example which contribute around 25% of results.

Similarly, if we are looking at very small sample sizes in a statistically noisy environment, then we are often going to get extremes of good or bad percentage based outcomes through chance.

Manchester United's win% without Smalling is zero%, he's missed one game all season, the 2-1 loss at Bournemouth.

Even more damning, we could point out that three of Everton's Osman inspired wins, 6-2 v Sunderland, 4-0 v Villa and 3-0 v Stoke had already been largely completed when he entered the field of play.

He played for one minute at Stoke, 16 against Villa and 12 against Sunderland, during which no further goals were scored or to be fair conceded. But it is a performance that manager, Roberto Martinez could almost certainly have replicated had he chosen to sub himself on rather than turn to Osman. Thus making himself a prime candidate to for Everton's most irreplaceable player under The Telegraph's deeply flawed methodology.

Familiarity with your data can help to avoid such faintly ridiculous conclusions and pushing Osman into the six games or more requirement on the basis of sixty seconds plus injury time at Stoke suggests that this particular "data cruncher" wasn't.

But another way to avoid publishing nonsense under the guise of stats is to spell out your conclusion without recourse to any of your data driven evidence.

"Osman's win% is 67%" sounds good, but "Based on Leon Osman's six Premier League appearances, five as a sub and one as a subbed off starter, I conclude that he is the player Everton cannot do without" should have been sufficient to spike this depressing addition to the analytics portfolio before it saw the light of day.

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