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The Fenwick Number
by PuckStopsHere on 08/23/09 at 11:25 AM ET
Comments (3)
I have been taking my usual look at sabermetrics and hockey this summer. I have spent most of the time looking at the Corsi Number. The Corsi Number is essentially an alternative to +/- ratings. Instead of using only goals scored to tally ratings, it uses all shots directed at goal (shots on goal, missed shots and blocked shots). This makes the numbers much larger and removes statistical noise to a better degree than +/- does. Corsi is a good judge of puck possession of players. Players with high Corsis tend to dominate in puck possession and those with low Corsis tend to have their opponents dominating in puck possession.
Corsi is not the only alternative to +/- that is used in this manner. Another method, which is less common, is the Fenwick Rating. It is named for Matt Fenwick from the Battle of Alberta blog. He factors out blocked shots from a Corsi Rating to include only shots on goal and missed shots.
Is this an improvement on Corsi? Does the removal of blocked shots better correlate with winning games? Does the reduction in the number of events cost in terms of increased statistical noise? Do the same players rank and the top and bottom in Corsi and Fenwick ratings or is there a systematic difference in these rankings? In the next few posts, I intend to address these issues.
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Comments
I might as well pop up to clarify:
Back when some of us were batting around Corsi and its value, I pushed to exclude blocked shots, kinda under this rationale:
- the idea is that Corsi serves as a proxy for scoring chances for and against
- if you have two very similar players with comparable shots and misses for/against, it seems to me that in that context, the guy persistently blocking extra shots is preventing scoring chances, whereas the guy persistently getting his shots blocked is failing to create scoring chances. Which I thought should be reflected in any stat whose purpose is to serve as a proxy for scoring chances for/against
- part of the rationale derives from being a Flames fan; the Flames persistently have a very high Blocked Shots For/Against ratio, relative to Shots ratio and Misses ratio. To me it’s straightforward that this “extra-high” Blocks ratio is not reflective of better scoring chances.
Anyway, I really can’t recall if either measure correlates better with goals for & against. I believe Corsi is a very slightly marginally better predictor of future EV+/-.
And, based on Dennis’ work last season at mc79hockey.com, Corsi (or Fenwick) most definitely correlates to scoring chances For & Against. Highly.
Posted by Matt Fenwick on 08/31/09 at 10:57 AM ET
my 2 cents,
If a team has 40 shots total, that either miss the net orare all stopped by the goalie, and the other team has 20 shots total of which 9 are blocked and 1 goes in the net, then the other team won. The guy that scored the goal has made a better shot than anyone else even if he played 5 shifts on 4 of which he had 9 turnovers.
these sabermetricks and corsi’s and fenwicks are all useless at that point.
We all know the other team played better, we all know why they lost.
Posted by fish on 09/02/09 at 02:25 AM ET
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C’mon, seriously? Your look at the Sabermetrics sucks hardcore. Nobody cares. Does Puck Daddy have any room over at yahoo?
Posted by yreland from Van Dieman's Land on 08/23/09 at 04:44 PM ET