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Hockeymetrics: A Look at Alternative Plus/Minus Ratings

I'd be remiss if I didn't give credit to Vic Ferrari, who posts the Corsi and Fenwick numbers at his site, timeonice.com

From a hockey metrician's point of view, traditional plus/minus is probably THE one stat that will elicit a collective facepalm from the entire hockey metrics community.

And for good reason.

Just look at the Stars penalty kill as a prime example of how useless a stat it's been. The struggles of that unit have been well documented. Yet, if you look at the individual stats, you'll see that Nicklas Grossman leads the club with a +11 rating while Robidas has a +7.

And it's all because those problems on the penalty kill have absolutely no effect on plus/minus. Consequently, if you're a vital part of the overall success on a power play unit, you don't get any credit.

So it's not surprising to see how traditional plus/minus has provided the impetus for other plus/minus ratings. This week, we'll take a look at three such ratings systems and discuss the pros and cons.

Corsi Ratings: Developed by Buffalo Sabres goaltender coach, Jim Corsi.

Japers' Rink has an excellent introduction to Corsi Ratings from last season.

It measures all shots taken in even strength situations, excluding empty net situations, that are either goals, shots on goal, blocked, or missed the net. As you might guess, you get a plus rating if your on the ice when your team scores an even strength goal, puts a shot on net, block a shot, or your opponent misses the net. Consequently, you get a minus if your team surrenders an even strength goal, puts a shot on net, blocks a shot, or if a shot from your team misses the net.

The pros of such a system are that they measure quite a bit more than traditional plus/minus. More to the point, it tries to measure how well your team can apply pressure to the opposition and how well it handles pressure.

Unfortunately, Corsi numbers don't measure power play, short handed, and empty net situations. I understand why as it's almost impossible to correctly weight those situations against regular even strength situations.

Fenwick Ratings: Developed by Matt Fenwick from the blog,  Battle of Alberta.

His criteria is almost the same as Corsi's, except it takes blocked shots out of the equation.

Chris Apple and Marc Foster plus/minus: Developed by one of my friends and one of his data analytical friends almost a decade ago. They wrote a series of articles in 2001 that appeared in CNN/SI that you can check out here.

In their system, you get a plus rating for all goals scored by your team when you're on the ice, no matter if it's an even strength tally, short handed tally, or power play goal. Consequently, you get a minus if you're on the ice when your team gives up a goal.

The pro of this system, obviously, is that it takes into account ALL goals that are scored in the course of a game, regardless if it's even strength, on the power play, or shorthanded.

Of course, it does treat all goals the same and thus, doesn't weight even strength or shorthanded goals above power play goals. But to their credit, Marc and Chris also developed a separate weighted goals system that weights goals more that give a team the lead or tie a game than ones scored in garbage time. But that's for another discussion.

So now that you know how each metric is measured, let's look at the Stars best and worst players by each plus/minus rating system after the jump.

Star-divide

First, let's look at the Corsi ratings. You'll notice the secondary header row labeled DAL and OPP for Goals, Saved Shots, Missed Shots, and Blocked Shots. I labeled them the way I did so you'll see them from an offensive POV.

That is, where it says 48 saved shots for Dallas on Brad Richards' ledger, it means that the Stars fired 48 shots that got through on goal and were saved while Richards was on the ice. Consequently, the 41 under Opp on Saved Shots means the Stars gave up 41 shots on goal that were saved while Richards' was on the ice.

      Goals Saved
Shots
Missed
Shots
Blocked Shots Corsi
+/-
      Dal Opp Dal Opp Opp Dal Opp Dal
91 C RICHARDS, BRAD 8 4 48 41 24 20 31 14 32
5 D NISKANEN, MATT 1 4 48 39 27 19 30 17 27
44 D WOYWITKA, JEFF 2 2 29 15 18 15 16 13 20
9 C MODANO, MIKE 0 0 11 4 4 0 3 3 11
3 D ROBIDAS, STEPHANE 12 7 66 69 29 41 38 20 8
17 C PETERSEN, TOBY 2 2 41 38 20 17 14 15 5
58 L WATHIER, FRANCIS 0 0 4 2 1 2 3 0 4
20 C SUTHERBY, BRIAN 4 2 39 42 13 17 19 11 3
21 L ERIKSSON, LOUI 7 4 57 50 16 32 32 24 2
29 C OTT, STEVE 4 4 33 35 21 18 13 14 0
18 L NEAL, JAMES 8 5 49 51 21 34 27 17 -2
26 R LEHTINEN, JERE 0 1 12 8 2 7 8 8 -2
11 C GAGNON, AARON 1 0 2 4 0 3 0 1 -5
15 C LINDGREN, PERTTU 0 1 4 7 2 2 0 2 -6
10 L MORROW, BRENDEN 9 5 51 64 26 39 38 24 -8
2 D GROSSMAN, NICKLAS 14 6 64 72 25 48 35 21 -9
96 L BRUNNSTROM, FABIAN 4 6 44 42 15 20 14 23 -14
23 C WANDELL, TOM 5 3 44 51 23 32 21 22 -15
63 C RIBEIRO, MIKE 9 7 51 71 26 38 37 29 -22
14 L BENN, JAMIE 8 1 36 53 22 37 23 21 -23
13 R BARCH, KRYSTOFER 1 4 25 41 14 25 15 13 -28
28 D FISTRIC, MARK 4 5 27 44 7 21 13 15 -34
6 D DALEY, TREVOR 7 7 68 90 32 48 42 43 -39
37 D SKRASTINS, KARLIS 4 8 62 74 29 39 23 37 -40

 

No big surprise that Richards is leading here. His line has been the most dominant of all the Stars' lines this season. What sticks out to me, however, is Jeff Woywitka's high rating versus Trevor Daley's low rating.

The 90 shots on goal allowed this season when Daley's been on the ice in even strength situations far and away leads the team. Of course, he also leads the team, far and away, in ESTOI with 186:25. The second highest total in that department belongs to Nicklas Grossman with 160:49.

Also of interesting note is Jamie Benn's -23 rating, despite being on the ice for 8 Stars' goals versus 1 total from the Stars' opponents.

OK, let's take out blocked shots and see what we get with the Fenwick Ratings:

        Goals Saved
Shots
Missed
Shots
Fenwick
+/-
        Dal Opp Dal Opp Opp Dal
6 44 D WOYWITKA, JEFF 2 2 29 15 18 15 17
  91 C RICHARDS, BRAD 8 4 48 41 24 20 15
9 5 D NISKANEN, MATT 1 4 48 39 27 19 14
1 9 C MODANO, MIKE 0 0 11 4 4 0 11
9 17 C PETERSEN, TOBY 2 2 41 38 20 17 6
6 29 C OTT, STEVE 4 4 33 35 21 18 1
1 58 L WATHIER, FRANCIS 0 0 4 2 1 2 1
2 26 R LEHTINEN, JERE 0 1 12 8 2 7 -2
1 11 C GAGNON, AARON 1 0 2 4 0 3 -4
1 15 C LINDGREN, PERTTU 0 1 4 7 2 2 -4
9 20 C SUTHERBY, BRIAN 4 2 39 42 13 17 -5
  96 L BRUNNSTROM, FABIAN 4 6 44 42 15 20 -5
10 21 L ERIKSSON, LOUI 7 4 57 50 16 32 -6
10 3 D ROBIDAS, STEPHANE 12 7 66 69 29 41 -10
10 18 L NEAL, JAMES 8 5 49 51 21 34 -12
10 23 C WANDELL, TOM 5 3 44 51 23 32 -14
10 10 L MORROW, BRENDEN 9 5 51 64 26 39 -22
10 2 D GROSSMAN, NICKLAS 14 6 64 72 25 48 -23
10 14 L BENN, JAMIE 8 1 36 53 22 37 -25
10 37 D SKRASTINS, KARLIS 4 8 62 74 29 39 -26
10 13 R BARCH, KRYSTOFER 1 4 25 41 14 25 -30
10 63 C RIBEIRO, MIKE 9 7 51 71 26 38 -30
7 28 D FISTRIC, MARK 4 5 27 44 7 21 -32
10 6 D DALEY, TREVOR 7 7 68 90 32 48 -38

 

Woywitka shoots to the top of the charts for one. But what stood out to me is that with blocked shots in the equation, Stephane Robidas is a +8 in the Corsi Ratings. Take out blocked shots and he's a -10 player in Fenwick Ratings.

Now onto the Foster/Apple total plus/minus ratings:

 

      ESGF PPGF SHGF TGF ESGA PPGA SHGA TGA TES
+/-
TPP
+/-
TSH
+/-
T
+/-
18 L NEAL, JAMES 9 3 1 13 5 0 0 5 4 3 1 8
10 L MORROW, BRENDEN 9 4 0 13 6 1 0 7 3 3 0 6
63 C RIBEIRO, MIKE 10 5 0 15 7 2 0 9 3 3 0 6
91 C RICHARDS, BRAD 9 5 0 14 4 4 0 8 5 1 0 6
2 D GROSSMAN, NICKLAS 15 0 1 16 5 6 0 11 10 -6 1 5
14 L BENN, JAMIE 8 2 0 10 5 0 0 5 3 2 0 5
21 L ERIKSSON, LOUI 9 4 0 13 6 2 0 8 3 2 0 5
3 D ROBIDAS, STEPHANE 14 2 0 16 6 6 0 12 8 -4 0 4
20 C SUTHERBY, BRIAN 3 1 0 4 0 1 0 1 3 0 0 3
9 C MODANO, MIKE 0 1 0 1 0 0 0 0 0 1 0 1
15 C LINDGREN, PERTTU 0 0 0 0 0 0 0 0 0 0 0 0
17 C PETERSEN, TOBY 3 0 1 4 2 2 0 4 1 -2 1 0
28 D FISTRIC, MARK 2 0 0 2 2 0 0 2 0 0 0 0
58 L WATHIER, FRANCIS 0 0 0 0 0 0 0 0 0 0 0 0
6 D DALEY, TREVOR 8 2 1 11 9 3 0 12 -1 -1 1 -1
11 C GAGNON, AARON 0 0 0 0 0 1 0 1 0 -1 0 -1
13 R BARCH, KRYSTOFER 1 0 0 1 2 0 0 2 -1 0 0 -1
26 R LEHTINEN, JERE 1 0 0 1 1 1 0 2 0 -1 0 -1
29 C OTT, STEVE 3 2 0 5 4 2 0 6 -1 0 0 -1
37 D SKRASTINS, KARLIS 8 0 0 8 6 3 0 9 2 -3 0 -1
44 D WOYWITKA, JEFF 3 0 0 3 3 1 0 4 0 -1 0 -1
96 L BRUNNSTROM, FABIAN 4 0 0 4 5 0 0 5 -1 0 0 -1
5 D NISKANEN, MATT 1 4 0 5 6 2 0 8 -5 2 0 -3
23 C WANDELL, TOM 4 0 0 4 5 3 0 8 -1 -3 0 -4

 

Remember when I said Grossman and Robidas were +11 and +7 in traditional plus/minus ratings at the beginning of the post? Well factor in the troubles of the penalty kill, and they're +5 and +4 ratings respectively with James Neal and Brenden Morrow taking the top spots with Brad Richards not far behind.

So what have we learned?

For one, there's no such thing as one metric that's going to perfectly measure a player. And any variation of plus/minus will validate that point. But what it does do is expose new strengths and weaknesses in an individual player's game.

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These don't work

+/- isn’t a perfect metric, but it does pretty successfully measure what it’s intended to measure.

You can’t include PP goals in +/- because then you’re basically penalizing your penalty killers statistically for being good defensively. PKs get scored on, it’s a fact of life. Even if you’re REALLY good on the PK, you’re still going to get scored on while killing a penalty exponentially more often than you’re going to score goals. The opposite is also true, PP guys, who are frequently terrible in +/- outside of the extra man situation, would suddenly be getting statistical rewards.

Blocked shots and all that is just too much to try and track and it introduces a lot of “noise” into the information that +/- otherwise tells us.

+/- is merely a metric that tells us how defensively responsible a player is during situations where the teams should theoretically be even. I think the strongest argument for keeping +/- the way it is is to look at the players who’ve historically led the league in +/-. The leaders are almost always the people we think they would be, the best defensemen and Selke winners/candidates.

+/- has one job that it does well. Trying to work PPs/PKs into it would be like trying to discount PP goals in GAA for goalies. Unnecessary, overcomplicated, and ultimately less useful than the original stat.

by HoboMaster on Oct 23, 2009 1:16 PM CDT reply actions  

Take it with a grain of salt.

I’ll argue that the metrics discussed in this post do work. Like the +/-, they’re not perfect; but like +/-, they do serve a particular purpose and can provide beneficial information; especially when used in conjunction with other metrics. In the end, you’re still trying to express defensive responsibility in numerical terms — it’s never going to be an absolute science.

Some people take this even further and bringing Quality of Competition into the mix. It’s fair to consider, but then you’re trying to numerically express something that can’t be expressed numerically (defensive responsibility) based on something else (QoC) that cant really be expressed numerically.

by colbymulkey on Oct 23, 2009 2:04 PM CDT up reply actions  

Great stuff Brandon

Though, the ones that make Niskanen and Woywitka look good are quite shocking ;)

by Brad Gardner on Oct 23, 2009 3:31 PM CDT reply actions  

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