by PuckStopsHere on 07/17/09 at 03:46 AM ET
In this summer’s look at sabermetrics and hockey, I have been looking at the Corsi Number as an alternative to +/-. Corsi Numbers are the difference between shots directed at the goal (shots on goal, missed shots and blocked shots) for and against when a player is on the ice in five on five situations. The benefit is that they encompass a lot more events than +/- does. However, whether or not it is a better or comparable series of events is somewhat of an open question.
I have calculated the Corsi Numbers for all 30 teams in the NHL. These can be compared to team +/- ratings.
|Detroit Red Wings||1||+918||5|
|San Jose Sharks||5||+406||10|
|New York Rangers||6||+405||23|
|New Jersey Devils||7||+301||3|
|Columbus Blue Jackets||9||+199||8|
|Los Angeles Kings||11||+105||27|
|Toronto Maple Leafs||12||+80||25|
|St Louis Blues||19||-251||22|
|Tampa Bay Lightning||20||-262||28|
|New York Islanders||29||-513||30|
It is clear that Corsi Numbers do increase the separation between teams. There is an over 1500 point spread between the highest Corsi (Detroit) and the lowest (Phoenix). With +/- this spread is slightly over 100 points. That aim of Corsi Numbers is clearly satisfied. However, it isn’t clear how similar what Corsi and +/- measure is. The order of teams in the two rankings is changed significantly. In general, good teams have top rankings and poorer teams have weaker rankings with both systems, but there are some rankings that seem a bit odd (or interesting). The Stanley Cup champion Pittsburgh Penguins were the 21st team in Corsi in the regular season. That is awfully low isn’t it? The +/- leading Boston Bruins fall to 13th in Corsi. The main difference here is that Corsi looks at shots and +/- at goals. Since Boston had the best goaltending in the league, there is a significant difference between the two. The worst Corsi ranking for a playoff team was Philadelphia who finished 24th. Does this show something was wrong with the Flyers or with Corsi rankings? The best ranking for a non-playoff team was Los Angeles, who finished 11th. Toronto was 12th. Toronto finished ahead of Boston on the Corsi list. Who would have predicted that?
The +/- list better scales with the NHL rankings. Of the top 16 on the +/- list, 13 made playoffs. Florida, Edmonton and Buffalo are the exceptions. The teams with lower +/- ratings that made playoffs were Montreal (17th), St Louis (22nd) and the New York Rangers (23rd - a Corsi success story finishing sixth). More work has to be done to properly compare +/- and Corsi and make more sense of their differences. That will come in a further post.
Looking at the Corsi rankings, we see that the best Corsi teams were better than the worst Corsi teams were bad. Detroit, Calgary, Washington and Chicago had higher positive team Corsi Numbers than the worst team (Phoenix) was negative. This explains why these teams dominated the individual player’s top 20 rankings. They claimed 15 of the top 20 positions. This also explains why the worst 20 rankings are spread out between many teams.
With these numbers, we can begin to adjust Corsi Rankings or individual players and see if that teaches us anything significant,
Team Corsi Numbers do not scale as well with team success as team +/- ratings do. How meaningful is their difference? Is the fact that Corsi Numbers are much bigger useful enough to overcome any differences? These are questions I will attempt to address in the future.
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