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Advanced Metric Frequently Asked Questions #3: What is a Corsi Number?

So what's a "Corsi Number" and why is it so important in hockey?

Tom Szczerbowski-US PRESSWIRE

I hope you've had a chance to read Part 1 and Part 2 of the statistical FAQ I've been working on. Part 3 will focus on a statistic that Oilers blogger Vic Ferrari picked up on several years ago: the "Corsi Number." The statistic itself likely comes from inside the Buffalo Sabres organization, and their goaltending coach, Jim Corsi, has received credit for it.

In a nutshell, the Corsi Number is the shot differential while a player was on the ice. This includes not just goals and shots on goal, but also shots that miss the net, and in some formulations, blocked shots. In other words, it's the differential in the total number of shots directed at the net.

This metric was presumably adopted by the Sabres because it's a better indicator of a team's play than goals for and against, which are highly-driven by factors outside of a team's control. Shot volume is much more a function of a team's ability, and a much better predictor of future performance than goal-scoring metrics - in other words, there is basically no such thing as a team that shoots efficiently, just teams that get a lot of shots on goal...or not. Tyler Dellow has much more on this subject here. And Vic Ferrari discusses the "consistency" that underlies goal scoring, scoring chances and the Corsi Number.

You can see the 2008-09 Corsi leaders here. Anaheim's Perry/Getzlaf/Ryan unit was the best relative to their teammates, while Detroit's top two lines and anyone who played with Alexander Ovechkin were at the top of the raw numbers. At the bottom end, we had a bunch of Islanders and Coyotes leading the raw numbers, while the worst relative Corsi belonged to, unsurprisingly, Travis Moen, Rob Niedermayer, Jay Pandolfo, Sami Pahlsson and John Madden. The 2007-08 numbers don't look a whole lot different, with Detroit and Washington at the top again, while LA and Atlanta were at the bottom.