Jul 192011
 

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.

  12 Responses to “Some Names for Gabe”

  1.  

    David,

    I banned you from my site because you spent all of your time picking fights with people and because when other commenters pointed out legitimate concerns with your claims, you reused to even consider them.

    We’ve been over this territory before, and what you’ve written here is both intellectually-dishonest and a pretty feeble attempt to bait me and others into commenting at your site. It also confirms that we were justified in not reinstating your membership.

  2.  

    I am not sure what is intellectually dishonest. Someone challenged you regarding the fault with corsi that some players can influence shooting percentage and you came back with ‘name the players.’ As usual, when someone actually accepts your challenge and names players you come back with a bash the attacker response and avoid the actual discussion. The only thing I am surprised is that you didn’t come back with something so immature as “Vokoun! Vokoun! Vokoun!” as you have done before.

  3.  

    Johnson,

    I am not going to argue with you. You wrote that Tomas Vokoun was a bad goaltender because his teammates had a low shooting percentage when he was playing. This is a patently stupid claim and it was easily shown to be false. You’re intellectually dishonest because you never owned up to your mistake; instead, you’ve repeatedly tried to turn your mistake around on me.

    If you appeared to be interested in honest inquiry, you would find that people – myself included – are more willing to listen to you. But you’ve positioned yourself as merely someone who says black when I say white. That’s why you’re banned from my site and why anyone who ever comments on your site is so annoyed with you.

    •  

      You know as well as I that I never said that about Vokoun. Furthermore, I have addressed Vokoun here as you requested but you took any of my comments into consideration. But I guess we find out his worth next year now that he is on a good team.

      As for honest inquiry, whenever anyone questions corsi with respect to shooting percentage your response is prove it, or give me names. I’ve shown it (as have others), I’ve given you names (as have others) but you have ignored them all and then have a hissy fit about something you interpreted I said about Vokoun a year ago but in reality I never said. So, do you believe that players have no ability to drive shooting percentage? If that is what you believe, how do you explain the differences in on ice shooting percentage of say Sidney Crosby vs Travis Moen over the past 4 seasons?

      Let’s have an honest straight up discussion here.

      •  

        To quote you directly: “Vokoun’s record because his won-loss record (79-80-25) is notably worse over the past 3 seasons than his backups (32-22-8). That can’t be a sign of an elite goalie”

        I’m going to remind you of this one last time. Forget that everybody laughed you out of the building for even thinking that goaltender winning percentage is meaningful, and forget that you need to compare Vokoun to league-wide replacement level, not his own backup – I showed you that it was because Florida had a lower shooting percentage *for* while Vokoun was in net, and that (not surprisingly) goaltenders do not drive shooting percentage at the other end of the ice.

        This is the core of your dishonesty. You’ve never faced up to this moronic mistake in your analysis and so it’s a complete waste of my time to even engage you on any new topics because you just never learn anything.

        •  

          I happen to think that an elite goalie, even on a weak team, will put up a decent won-loss record (see Bryzgalov who probably isn’t even elite). I put his won-loss out there as evidence that maybe there is more to the story than his save percentage indicates and maybe there is more to the story than save percentage is telling us. How can a goalie so good, not help his team win?

          If you look around here I have shown that Vokoun has played against teams that are generally stronger defensively (hence his teams weaker shooting percentage when he has been in goal) but somewhat weaker offensively (hence Vokoun’s inflated save percentage). This would explain the discrepency between Vokoun’s poor win percentage and his stellar save percentage. It shows why Vokoun is probably not as good as his save percentage indicates.

          But of course, to someone that believes that treating every shot as equal is just fine, this makes zero sense. This isn’t a viable explanation and Vokoun must be god of all goalies because of his stellar save percentage every year and the team in front of him just happen to play poorly every time he is in net.

          •  

            You should stop deleting my responses. Why put my name in the title of your post if you don’t want to hear from me?

          •  

            If you have something useful to say I won’t delete it. If you are going to resort to name calling and non-hockey stupidity you betcha, I’ll delete it.

  4.  

    Driving and Suppressing Shot Quality as a concept doesn’t make a lot of sense to me on the basis of what I’ve seen written about it and the work I’ve done on my own.

    Players take more shots from certain areas of the ice and thus tend to have higher shooting percentages. Gabe’s work that I’ve seen has shown that only Tanguay and Kovalchuk have consistently higher shooting percentages than their shot locations would predict.

    I’d like to see a move towards Delta SOT away from Corsi, because it factors in shot location and number of shots… but that data isn’t easily available and I haven’t had the time to run the numbers myself.

    I know Tom Awad did this stuff already for the few years before this past season, so there IS data out there (to be scraped from NHL .XML files)… but yeah… this debate is amazingly focused on one statistic that has some inherent flaws (that are often acknowledged).

    •  

      I am pretty dubious about the overall effects of shot location. I don’t think they are significant. More important I believe are the circumstances leading up to the shot (i.e. turnover, cross ice pass for a quick one-timer, etc.) and the quality of the shooter. Research from Tom Awad backs this up. See http://www.puckprospectus.com/article.php?articleid=625 and especially the last chart where he estimates goal +/- due to shots, shot location and finishing ability.

      His conclusions are:
      “The unmistakable conclusions from this table? Outshooting, out-qualitying and out-finishing all contribute to why Good Players dominate their opponents. Shot Quality only represents a small fraction of this advantage; outshooting and outfinishing are the largest contributors to good players +/-. This means that judging players uniquely by Corsi or Delta will be flawed: some good players are good puck controllers but poor finishers (Ryan Clowe, Scott Gomez), while others are good finishers but poor puck controllers (Ilya Kovalchuk, Nathan Horton). Needless to say, some will excel at both (Alexander Ovechkin, Daniel Sedin, Corey Perry). This is not to bash Corsi and Delta: puck possession remains a fundamental skill for winning hockey games. It’s just not the only skill.”

      And looking at the ‘good players’ line we see that finishing ability is +0.22, shot location is +0.04 and shot differential is +0.15. In percentages the goal differential is 53.6% finishing, 36.6% shot differential and 9.8% shot location. Based on that, finishing ability is more than half of what makes good players better than their opponents. Similar, but opposite numbers, exist for 4th tier players.

      This isn’t inconsistent with correlations I have produced that show shooting percentage correlates with goal rates better than shot/corsi/fenwick rates. By using corsi, or even Delta SOT, you are eliminating about half of what goes into scoring goals.

      •  

        There’s a bit of a problem with correlating shooting percentage to goals, because goals are PART of the statistic. Obviously higher shooting percentage will correlate positively with higher goal rates, because the goal rate is goals/game or goals/60, while shooting percentage is goals/shots…

        Shots remain outside the goals/game or goals/60 calculations so there’s no effect of including the same statistic and attempting to correlate them.

        What you’re getting is similar to saying the diameter of a sphere is correlated to it’s volume… obviously it is.

        Nobody is saying shooting percentages don’t correlate… it’d be weird if they didn’t. The problem is, saying that guys score because they do isn’t really an explanation.

        I think the problem here is, you’re taking Awad’s work, and your own, and arguing that Corsi is “misleading” but it’s just one part of a larger toolbox. Denigrating someone’s hammer because it doesn’t work very well as a level is sort of unreasonable.

        Use corsi for what it is… a measure of puck possession skills.

        •  

          “There’s a bit of a problem with correlating shooting percentage to goals, because goals are PART of the statistic. Obviously higher shooting percentage will correlate positively with higher goal rates, because the goal rate is goals/game or goals/60, while shooting percentage is goals/shots…”

          People have been trying to explain this but I don’t get it. I can see how goals are in goals/60 and goals/shots and that would give you a sense that they are linked but they really aren’t. It’s like comparing kms with km/hr. One is a distance and one is a speed. They measure different things. Distance = speed * time. Goal/60 = shooting percentage * shots/60.

          “Shots remain outside the goals/game or goals/60 calculations”

          Not in the sense that goals/game = shots/game * shooting percentage.

          “Denigrating someone’s hammer because it doesn’t work very well as a level is sort of unreasonable.”

          Actually, the way I look at it is denigrating the use of a hammer with no handle when there is a perfect good whole hammer with a handle sitting right there ready to use.

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