Pages

Wednesday 4 July 2012

The EPL's Best Keeper.End of Season Version 2011/12.

This post on EPL keepers pre-empted the recent rash of posts extolling the virtues of regressing individual and team rate stats towards the mean of the sample from which they come.The original post has proved extremely popular,either indicating a large number of people are gripped by goal keeper stats or showing the value of a search friendly title.Whichever the reason,here's the end of season save percentage figures for all the keepers who pulled on a glove during the 2011/12 season.

The methodology is exactly the same as before.The larger the sample size the more the keeper's true ability will overshadow random chance and the smaller the sample size then the less confidence we can ascribe to an individual's save percentage figure.

This is best illustrated in the case of Ben Amos who managed to coax two shots out of Stoke City in his one and only appearance for Manchester United last season.He saved them both to record a 100% save percentage enough to put him at the top of every list of raw save percentage.While it will be comforting for United supporters that Amos managed to keep out Stoke's best efforts,he's unlikely to record anywhere near that save percentage in larger trials.So his numbers are regressed over 90% towards the mean of last year's goalkeeping save percentage of around 68%.The credit he receives for keeping a clean sheet lifts his regressed save percentage a couple of points above average.

All 2011/12 keepers are listed below,the regressed save percentage in the final column is the most indicative figure of each players likely true ability.

Best EPL Keepers 2011/12.


Keeper. Shots on
Target.
Saves. Observed
Save %
Regressed
Save %
De Gea. 131 102 77.9 76.4
Hart. 126 97 77.0 75.6
Lindergaard. 22 18 81.8 74.8
Stockdale. 58 44 75.9 73.7
Mignolet. 127 94 74.0 73.1
Vorm. 185 136 73.5 72.9
Friedel. 155 114 73.5 72.8
Schwartzer. 139 102 73.4 72.6
Cerny. 28 21 75.0 71.9
Hilario. 10 8 80.0 71.8
Begovic. 110 79 71.8 71.2
Amos. 2 2 100.0 70.8
Foster. 166 117 70.5 70.2
Howard. 135 95 70.4 70.1
Guzan. 28 20 71.4 70.0
Doni. 11 8 72.7 69.7
Hennessey. 238 165 69.3 69.2
Reina. 114 79 69.3 69.1
Krul. 165 114 69.1 69.0
Given. 143 98 68.5 68.5
Ruddy. 200 137 68.5 68.5
Cech. 123 84 68.3 68.3
Gordon. 6 4 66.6 68.0
Rudd. 9 6 66.6 67.9
Sorenson. 68 46 67.6 67.8
Westwood. 33 22 66.6 67.4
Jaaskelainen. 117 77 65.8 66.2
Al Habsi. 181 119 65.7 66.0
Kenny. 166 107 64.5 64.9
de Vries. 20 12 60.0 64.5
Bogdan. 100 63 63.0 64.0
Turnbull. 11 6 54.5 64.0
Szczesny. 133 84 63.1 63.9
Kean. 5 2 40.0 63.4
Tremmel. 2 0 0 63.0
Fulop. 3 0 0 60.7
Bunn. 14 5 35.7 56.2
Robinson. 167 71 42.5 45.7

While it's hardly a surprise that much of the EPL's keeping talent resides in Manchester,there is a definite practical use for the regressed numbers.As I've tried to illustrate in these  posts on crossing and shooting the regressed figure is a much better indicator of performance in subsequent seasons than is the raw unregressed rate.The table below illustrates 14 cases of goalies returning to EPL action from the 2010/11 to the 2011/12 seasons and it is the regressed rate from 2010/11 and not the actual observed rate that gives a better indication of 2011/12 performance in 12 out of the 14 occasions.

David Stockdale's numbers well illustrate this point.His 81% save rate was achieved over just 32 attempts.After regressing that figure almost 60% towards the mean his corrected rate falls to 75.2% very close to the actual save % he produced in 2011/12 from almost twice as many shots.

What's the Best Indicator of Future Goalkeeper Save Percentage.

Keeper. Observed
Save % 2010/11.
Regressed
Save % 2010/11.
Observed
Save % 2011/12
Is the 2010/11 Regressed % Closest to the 2011/12 %
David Stockdale. 81.3 75.2 75.9 Yes
Joe Hart. 77.1 74.2 77.0 No
Petr Cech. 75.0 73.5 68.3 Yes
Asmir Begovic. 75.0 73.5 71.8 Yes
Mark Schwartzer. 71.8 71.1 73.4 No
Ali Al Habsi. 70.5 70.2 65.7 Yes
Craig Gordon. 70.4 70.0 66.6 Yes
Wojciech Szcsesny 69.4 69.3 63.1 Yes
Pepe Reina. 69.0 69.1 69.2 Yes
Tim Howard. 69.0 69.1 70.4 Yes
Simon Mignolet. 67.6 68.1 74.0 Yes
Thomas Sorensen. 64.4 66.9 67.6 Yes
Brad Friedel. 64.4 65.5 73.5 Yes
Tim Krull. 57.8 61.9 69.1 Yes

2 comments:

  1. First of all, great blog, keep up the good work. I can't remember how I first stumbled across your stats but I've found it fascinating and your explanations are clear. Also I read the recent news articles on penalty shoot-out statistics which set off alarm bells about sample sizes - this was the first place I visited to see if someone else had queried it.

    Anyway, my question is about the regression method you use. From the first table, It appears that you have added 23.67 shots at the population mean save rate to each keeper's stats. Unless I have the method completely wrong, can you tell me how you arrived at this number? I understand the theory behind regression and the different variances, but my equations don't seem to come up with the right numbers.

    I don't mean to copy your work, just trying to learn.

    Cheers

    ReplyDelete
  2. Great work. It's a topic I've been looking into myself lately. Do you happen know what the r^2 for the observed 11/12% and the regression 10/11% is?

    ReplyDelete