@mc79hockey do you believe positive Corsi = more wins is 100% accurate?
— Cory West (@Westcory) December 4, 2013
I was asked this question in the context of talking about defencemen. I’m probably going to get more of this when a piece that I wrote about Brian Campbell and Tom Gilbert goes live so this is a sort of pre-emptive shot.
The short answer to this question is basically yes. As a defenceman piles up minutes, his GF% and his Corsi% becomes ever more tightly tied. I’ve put together a chart that summarizes this:
So for defencemen with at least 5000 minutes of 5v5 play between 2007-13, 73.5% of them saw goals scored at a rate that was within +/- two percentage points of their Corsi%. That’s pretty astonishingly tight. You can see, if you look from left to right, how the sample size increasing shrinks the difference between the Corsi% and the GF%. If Corsi% comes to equal GF% and we know that GF% comes to equal wins, then it’s pretty accurate to say that positive Corsi = more wins. These players who people imagine with a 55% Corsi% who give up so many ten bell chances that it overwhelms it don’t seem to exist.
There’s plenty of evidence that defencemen don’t significantly impact on shooting percentage or save percentage, although I confess to wondering if the best two or three defencemen don’t have an impact on save percentage. If that’s generally true, the only sensible way to evaluate their 5v5 play is on the basis of how they impact on the Corsis – the goals are basically noise in the short run.
This doesn’t mean that good Corsi = good defenceman. You want to try and figure out if the defenceman is causing the good Corsi or not. Sometimes, it’s pretty easy – Chara, for example, has a 54.8% Corsi% between 2007-13 on a team that’s a 52.1% Corsi% team overall. I have no difficulty in concluding that he makes them substantially better. Christian Ehrhoff has a 46.8% Corsi% this year on a Sabres team that is at 43.3% overall. I suspect that he’s a pretty good player.
There’s a layer of stuff below Corsi% that we don’t fully understand yet. When we do, we’ll be able to say with much more accuracy than we can now which players are driving the play and which are along for the ride. With that being said, we can draw some pretty sound conclusions now by carefully examining data. As long as we look at the right stuff.Email Tyler Dellow at email@example.com