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EPL: Persistence of Possession

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In our NHL analysis, we spend a lot of time looking at shot ratios (Corsi, Fenwick, etc...) as a proxy for puck possession or offensive zone time. These are fairly consistent quantities from year-to-year, and teams retain nearly 60% of their performance:

Yoy_nhl_shooting_medium

Compare that to ball possession in soccer:

Yoy_passing_medium

EPL teams have virtually zero year-to-year variation in ball possession. If you know how a team did last year, then you've got a pretty good idea of how they'll do next year. There are other elements - goaltender talent, shooting talent, and a whole lot of luck - but teams are essentially stuck where they are. Here are teams that been in the EPL over the last four seasons:

Avg >40 >45 >50 >55 >60 Max-Min
Chelsea 63.86 4 4 4 4 4 2.17
Man Utd 61.73 4 4 4 4 4 2.92
Arsenal 61.62 4 4 4 4 4 2.30
Liverpool 61.09 4 4 4 4 2 4.13
Spurs 53.66 4 4 4 1 0 3.36
Man City 49.88 4 3 3 0 0 9.53
Everton 49.84 4 4 2 0 0 6.50
West Ham 49.49 4 4 1 0 0 4.87
Blackburn 48.09 4 3 2 0 0 11.73
Fulham 47.78 4 3 1 0 0 8.16
Man City 47.43 4 4 0 0 0 3.24
Aston Villa 46.85 4 4 0 0 0 4.39
Wigan 46.46 4 2 1 0 0 10.68
Bolton 41.28 2 1 0 0 0 13.10

Obviously there are structural reasons why Chelsea, Man United, Arsenal and Liverpool dominate play, but most teams are trapped in a very small range of performance regardless of year-to-year changes they make to their teams. It's unfortunate that we don't have passing and possession data for the NHL - we could see if this is an equivalently-persistent skill in hockey. It seems unlikely, but having pass information as opposed to just shots as we do today would leave us much less at the mercy of luck.