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It All Started With Jim Corsi

from Kevin McGran of the Toronto Star,

The first thing Jim Corsi wants the world to know? He didn’t invent the Corsi stat.

If that is a mystery to you, maybe you don’t know who Corsi is or what the stat named after him represents. If so, you haven’t been paying attention to the statistics revolution in the NHL that has made the last two months hockey’s summer of analytics.

Throughout the NHL, teams like the Maple Leafs, Devils, Penguins and Oilers have been gobbling up executives and statisticians who can walk them through what the blogosphere has been promoting for years — what some call analytics, or advanced statistics.

It’s growing social-media-powered movement with a fanatical following that believes there are means to measure a hockey player’s contribution to a team beyond the obvious stats of goals, assists and ice time.

And it all started with Corsi, hired this summer as goalie coach of the St. Louis Blues; he was previously with the Buffalo Sabres. He might otherwise be known as the WHA goalie who got a cup of coffee in the NHL with the Edmonton Oilers and, though born in Montreal, played on Italy’s national team.


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does it not bother anyone else that the basic assumption of the Corsi stat is that all shots at 5-on-5 are equal? meaning, that a short from the blue line on goal is weighted as the same as shot on goal after a rebound in the crease. We look at shots because - obviously - you can’t score if you don’t shoot the puck (excluding own goals, deflections, etc.). However, to get a more accurate and dare I say appropriate indicator of what Corsi is attempting to measure, you really need to weigh the shots based on its probability (likelihood) of scoring (in crease, top of circle, rebound, etc.), the level of competition on the ice at the time of the shot, the game situation at the time of the short (is the team leading the game by a large margin or are they in the last minute of play down by a goal and throwing everything they can at the goalie?), etc. I understand the desire to capture this data and to analyze it, but you just can’t take the easy way out and do something that has little substantive meaning to the game. Sure Corsi is correlated with winning teams mostly because teams that shot more are more likely to score than those that shoot less. I’m curious to hear your thoughts.

Posted by scooter on 08/10/14 at 10:37 PM ET

shazam88's avatar

The overriding point is that Corsi is a decent - but not perfect - proxy for puck possession, and puck possession correlates with a lot of good things, like winning. Certainly not all shots are not equal, but by using a larger data field (shot attempts as opposed to plus-minus or some generally unworkable shot-by-shot weighted evaluation), aberrations are smoothed out over time.  Additionally, Corsi and / or Fenwich are often filtered to remove noise from large leads (“Corsi close” iirc) so blowout games don’t necessarily play into things all that much.


Posted by shazam88 from SoCal on 08/11/14 at 03:56 PM ET

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Paul Kukla founded Kukla’s Korner in 2005 and the site has since become the must-read site on the ‘net for all the latest happenings around the NHL.

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