June 28 2012 02:29PM
Whatever tendency certain players might have for driving their team to get more scoring chances than a simple shot differential predicts is small and swamped by random noise. This suggests tracking scoring chances isn't adding much information to the readily available shot differential numbers.
That's from Eric on this very blog earlier this week. I'm willing to believe that, too. Over the course of the season, when I was tracking chances for Vancouver, I found that when the Canucks out-chanced a team, they were really not in a position to win the game all the time.
Looking at just even strength numbers, ahead. Since I can't get game-by-game scoring chance and shot totals without spending my entire summer hunched over my computer, I went back through all 82 Vancouver Canucks games that myself and Thomas Drance tracked this year.
Side-by-side, they produced some interesting results.
And, yes, the team's overall Fenwick number and scoring chance number formed a certain bond by the end of the year. The Canucks finished the season with a 51.7% Fenwick rate and a 50.3% scoring chance rate. That's a sizeable-enough difference, but if you look at the graph, both red and blue lines come together at about 34 or so:
That's over the course of the season.
I'm pretty well convinced that, after 82 games, judging players by scoring chance numbers versus possession numbers such as Corsi or Fenwick doesn't make a damn lick of difference.
However I split some of these games up. Since I was only looking at even strength, there's a possibility that there could be ties. Some games ended 2-2 or 1-1 in even strength goals, and I was looking for the team's win, loss or tie record at even strength to determine whether scoring chance statistics are better predictive than Fenwick.
|Shots 50% +||18||16||9||0.529|
|Chances 50% +||23||10||7||0.697|
|Both 50% +||13||8||7||0.619|
The Canucks did much better in games where they out-chanced the opposition rather than simply out-shot them. For sure, the out-shot record is variant on score effects, but it doesn't seem that scoring chances were affected so much by this.
What about games where the Canucks out-shot but didn't out-chance the opposition? They were 3-5-2 in those games:
|Shots, not Chances||3||5||2||0.375|
|Chances, not Shots||9||1||0||0.900|
Shot metrics, at least those that haven't been adjusted for score, are clearly not as good over small game samples for determining victories.
Another interesting thing to note is that the Canucks save percentage in games where they out-chanced their opponents' was .931. Their save percentage in games where they were out-chanced was .930. On offence, there was a bigger difference, 8.8% versus 7.4%, so I'm more inclined to think that there's some form of shot quality that exists on offence, but not so much on defence.
There's still some use to counting chances. Maybe they shouldn't be analyzed with as much rigour at the end of the season, since corsi will do the trick, but, again, on a single-game basis, at least for the Canucks, scoring chances seem score effect-neutral so you have more events with which to judge a player's performance.