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The Eye-Test Vs. Corsi: Canucks Game 1


JamesB

Eye-Test vs. Advanced Stats  

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12 hours ago, oldnews said:

ok will do - and can't be bothered to read beyond that - if that's your irrational response to a pretty straight forward and reasonable post ie nothing personal whatsover - a simple discussion of the meaning and merit of 'analytics'.

cheers.

And I guess that's why you only got through the first line of my other post without understanding the overall meaning.

 

But as with many things around advanced stats, it's not just one stat versus old fashioned scouting. It's using multiple stats in tandem with watching games to get a deeper picture of what might be happening with a player. Without them, you're just relying on how good each of your scouts are without any real validation.

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1. Most importantly, CORSI does not adjust for strength of competition, which is a huge factor. The difference between going up against the McDavid line and going up against the Edmonton bottom 6 is huge in terms of expected CORSI. The Sutter line was able to keep the McDavid line from scoring, forcing them into a lot of missed shots, blocked shots, and  low percentage shots, all of which count in CORSI. They did a great job. The Sedin line played the Edmonton bottom 6 about even -- which is not such a great accomplishment. There are some attempts to adjust for quality of competition but they are woefully inadequate. The explanation is long, but it is very hard to adjust properly for quality of competition. 

 

 

This entire paragraph makes me laugh.  Mainly because of all the whiners about the new guys should be line 1.  The Sedin's have fought against the toughest lines all their career and flourished.  Now the new blood is facing tougher competition and are looking flat.  Shows you really how good the Sedin's are and continue to be.  The will not go quietly into the night!

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On 10/9/2017 at 0:41 PM, JamesB said:

The Canuck game 1 provides a very good illustration of the contrast between using the "eye-test" to evaluate player performance and using advanced stats, particular shot metrics such as CORSI and FENWICK. Personally, I like some advanced stats but I do not like these shot metrics. Game 1 against Edmonton illustrates the problem. First, for anyone interested, the shot metrics are available here: https://www.hockey-reference.com/teams/VAN/2018.html#all_stats_adv_rs

 

The eye-test summary of the game runs as follows.

 

1. First, Travis Green,  the reporters (even Botchford), the players, and most of CDC thought that the Canucks played a good game against a good team. After all, the Canucks won the game and a lot of guys looked good doing it.

2. The first star of the game was Horvat, who scored two impressive goals and looked great -- fast, strong, high intensity.

3. The "second star" of the game was the Sutter line (with Dorsett and Granlund) who shut down arguably the best line in the NHL (with McDavid and Draisaitl) and scored a goal.

4. Markstrom let in a questionable first goal but was otherwise very good.

5. If there was a disappointment in the game for the Canucks it was probably the Sedin line (with Vanek) who looked slow out there and did not do much on the PP despite lots of PP time.

 

The CORSI (shot attempt) summary is completely different and illustrates the weakness of CORSI numbers. Here is the even strength CORSI summary.

 

1. The Canucks had a bad game, getting crushed by Edmonton on shot metrics.

2. The best Canuck line by far was the Sedin line. The top 3 forwards in CORSI were Daniel (61.5%), Vanek (57.1%), and Henrik (50%).

3. The worst Canuck line was the Sutter line. Their shot metrics were Granlund (22%), Dorsett (25%) and Sutter (26%).

4. The Horvat line was not much better: Horvat (32%), Baertschi (32%), Eriksson (33%).

 

This comparison illustrates my pet peeves about CORSI.

 

1. Most importantly, CORSI does not adjust for strength of competition, which is a huge factor. The difference between going up against the McDavid line and going up against the Edmonton bottom 6 is huge in terms of expected CORSI. The Sutter line was able to keep the McDavid line from scoring, forcing them into a lot of missed shots, blocked shots, and  low percentage shots, all of which count in CORSI. They did a great job. The Sedin line played the Edmonton bottom 6 about even -- which is not such a great accomplishment. There are some attempts to adjust for quality of competition but they are woefully inadequate. The explanation is long, but it is very hard to adjust properly for quality of competition. 

 

2. CORSI is usually reported for even strength play. But special teams are obviously very important. Factoring special teams in correctly is difficult. Once again, in this game, Sutter, Dorsett and Granlund were good on the PK. The Sedins did not play PK but they led the forwards in PP time and did not do much in that time.

 

3. Shot quality is obviously important. Generating low quality shots, missed shots, and blocked shots is obviously less valuable than driving the net (as Horvat did on his first goal) or getting close-in chances (as on Horvat's second goal). There are attempts to adjust for shot quality, but it is hard to do well. Horvat and Baertschi go not generate a lot of low quality chances but play hard to get high quality chances. This hurts their CORSI numbers.

 

The point of this post is not to criticize the Sedins. They have had great careers and I hope they have a good year this year. They were okay in the first game. And my point is not to criticize advanced stats. However, looking just at even strength CORSI is often very misleading. Getting good advanced stats is difficult. I am, for example, also not a fan of GAR (goals above replacement) or WAR (wins above replacement), largely because they fail to account for quality of competition (and quality of teammates). 

 

Stats I like include actual zone time metrics, defensive zone exit stats, and metrics based on high quality scoring chances. However, all of these should be adjusted for quality of competition and quality of teammates.

 

Any comments would be appreciated.

 

 

Stats are meant to be used together, hence graphs. 

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2 minutes ago, Where'd Luongo? said:

Stats are meant to be used together, hence graphs. (X/Y)

The only stat that really counts is wins v losses.  All these fancy stats, and eye tests mean zero unless the team is winning games.  If the team is losing more than winning then the team and the players are not good, in any way.

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10 minutes ago, Alflives said:

The only stat that really counts is wins v losses.  All these fancy stats, and eye tests mean zero unless the team is winning games.  If the team is losing more than winning then the team and the players are not good, in any way.

We use stats figure out what COMBINATION of players will increase OPPORTUNITIES. Stats are relevant, the NHL just hasn't figured out what stats to use yet. My guess is it will involve combining the entire line's stats, and using stats like:

 

- successful breakout/unsuccessful breakout * shooting percentage on the rush

- quality shots/toi (this requires a bit of analysis on each shot)

- passing percentage x (takeaways/giveaways)

 

Getting creative and making some new stats to help analyze will give you better insight as to why some lines work and others don't.

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On ‎2017‎-‎10‎-‎09 at 11:41 AM, JamesB said:

The CORSI (shot attempt) summary is completely different and illustrates the weakness of CORSI numbers. Here is the even strength CORSI summary.

 

1. The Canucks had a bad game, getting crushed by Edmonton on shot metrics.

2. The best Canuck line by far was the Sedin line. The top 3 forwards in CORSI were Daniel (61.5%), Vanek (57.1%), and Henrik (50%).

3. The worst Canuck line was the Sutter line. Their shot metrics were Granlund (22%), Dorsett (25%) and Sutter (26%).

4. The Horvat line was not much better: Horvat (32%), Baertschi (32%), Eriksson (33%).

 

This comparison illustrates my pet peeves about CORSI.

First off, CORSI isn't going to tell the whole story.  If you're looking for something that 100% accurately reads a team, game, player or whatever then it's a fool's errand as that doesn't exist.  The "eye test" is based on opinion and hockey knowledge, even the best of experts will have completely opposing opinions on games/players/teams and so on. 

 

So look at CORSI, take it in as part of the information that's used to paint the whole picture of what you're looking at.  It's not something that should have a ton of value put on it, and it's also something you can't disregard.  I agree there are weaknesses in any one stat summary especially if you're looking at just that one stat like CORSI.  

 

1. The Canucks had a bad game, getting crushed by Edmonton on shot metrics.

Canucks won and it was a great game to watch, very entertaining.  CORSI sees team A gets outshot by team B, who will win most of those games?  In that sense CORSI is just telling you who gave themselves the better chance to win the game.  

 

3. The worst Canuck line was the Sutter line. Their shot metrics were Granlund (22%), Dorsett (25%) and Sutter (26%).

In this sense your pet peeve is accurate because it doesn't take into account the fact that that line was playing against the best player in hockey.  CORSI doesn't care about Dorsett getting under the Oilers skin but those things affect the game.  

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