An interesting statistical debate sprung up today started by Tom Benjamin who wrote about his skepticism of the Corsi statistic. In it Tom comments on the fact that Ryan Kesler and Ryan Clowe ranked so highly in corsi in response to Greg Ballentine’s posts at The Puck Stops Here.
Greg’s examples, it seems to me, make a good case against the Corsi statistic. First, both the Kesler and Clowe stories tell us how much influence context has – neither Kesler nor Clowe could have done it playing on a different team or even playing in a different role on the same team. In other words, this is not really an individual statistic.
Of course, this got some in the Corsi crowd up in arms and states that Corsi can’t be used on its own without considering its context. Gabe Desjardin’s comments on Tom’s post with the following:
Corsi, like any other statistic, needs to be understood in the context of other factors. Sneering at it because, like any other simple statistic, it doesn’t provide a unified measure of a player’s complete value doesn’t contribute anything to the larger discussion of hockey analysis.
Ok, so I am glad we have that cleared up. Corsi is just a stat without meaning unless you consider the context. Oh good, now it is on par with nearly every other stat in hockey. Unfortunately people actually use corsi to actually draw conclusions about players.
Here is the thing that really irks me about some in the Corsi crowd. They just assume that shot quality doesn’t exist. An anonymous commenter using the name ‘Name’ writes the following:
Even the basis of corsi, that shot quality always evens out, so we just have to measure shot quantity, is inherently flawed. The strategies and styles some teams play lead to giving up a greater number of shots, but reducing quality ones, whereas some teams strive to block or prevent every single shot, no matter where it comes from. Therefore some players, just by playing on a certain time, will inherently be on the ice for more shots against. It doesn’t mean they’re giving up more quality scoring chances, or making lots of defensive mistakes, or failing to control play offensively.
To this comment Gabe comes back with his favourite response to any challenge put his way:
Name these teams and players. Thanks.
Now that is a fair response, unfortunately he ignores anyone who actually names these players. The reality is shot quality doesn’t even out. Some players drive shot quality and some players suppress it. Some players have a significantly different +/- than corsi +/- year in and year out. I gave an example the other day in Brendan Morrison. Here are some other names for Gabe to consider.
Some guys who can drive shooting percentage: Sidney Crosby, Marian Gaborik, Nathan Horton, Bobby Ryan, Martin St. Louis. Henrik and Daniel Sedin. Alex Tanguay. Jason Spezza.
Some guys who can suppress shooting percentage: Marco Sturm, Travis Moen, Tyler Kennedy, Taylor Pyatt, Shawn Thornton, Chris Drury, Jeff Carter. Torrey Mitchell. Kamil Kreps.
No one in the second group had an opposition shooting percentage above 7.6% in any single season over the past 4 years. Only a handful of times over the past 4 years has any of the players in the first list had an on ice shooting percentage below 9% and only Bobby Ryan’s 23 game 2007-08 season was below 7.6%.
Now, you’ll probably notice that the first group are all first line players who are expected to produce offense while the second group are mostly third line players asked to shut down the opposition. It’s difficult to suggest it was just luck that this is how things panned out. No, some combination of talent and style of play will affect your on ice shooting and opposition shooting percentages. And again it needs to be stated that shooting percentage is much more highly correlated with scoring goals than corsi.
Jeff Carter is an especially interesting case in that you can in no way argue that he has played in front of especially good goaltending that would drive down his shooting percentage against and yet he has a really slow shooting percentage and yet has one of the highest corsi against of any forward over the past 4 seasons (20.1 corsi events against per 20 minutes over the past 4 seasons ranks 300 of 310) but his goals against (0.753 per 20 minutes) is decidedly average or even slightly better than average (ranks 139 of 310).
So Gabe, those are some players for you to consider. I look forward to your response.