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Triumph

Yet Another Reason Why Plus/Minus Is Stupid

28 posts in this topic

(Cross-posted from Driving Play, figured it's relevant here)

Plus/Minus is often maligned by fancy stats types as not descriptive - it doesn't take into account the quality of competition or teammates. It doesn't acknowledge whether your team's goaltending is great, horrible, or somewhere in between. There's yet another reason why it's dumb - it describes game states that are not entirely relevant.

I took for my example the Devils. We all know they are having quite a bizarre season so far - 8-1 in shootouts, their record in regulation is a mere 10-15, but right now they're holding on to a playoff spot. More strange is their special teams play - they've scored a mere 17 power play goals, while allowing a whopping total of 11 short handed goals. Yet while shorthanded, they've only allowed 10 goals and have scored 7 short handed goals themselves. In addition, they've allowed 4 empty net goals and have scored none at even strength. All this has made the team plus minus even more useless than it already is, since as we know, plus/minus includes short handed and empty net goals.

Let's just look at the forwards' plus minus:

4DTjW.jpg

Looks pretty bad, right? But when we take out short handed goals for and against as well as empty net goals, it looks a lot different:

OTEUT.png

We see a lot of pluses where there were minuses before. If we were using +/- to talk about even strength play on the Devils, most players have a radically different even strength +/-. We might erroneously think that Ilya Kovalchuk is having a horrible season at even strength, but he's merely been average-ish. What are we even looking to describe when we talk about +/-?

Conclusion: Plus/Minus is stupid. Again.

Edited to fix tables

Edited by Triumph

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Yeah that's a good topic tri. As bad as people think kovys d has been, he's actually been fairly average ES, which came as a surprise to me.

Edited by SMantzas

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I don't think plus minus is stupid, just misleading at times. You really can only compare guys on the same team. But I don't get why you think SH goals shouldn't count against plus minus. Empty net goals, I agree on.

Edited by NJDevs4978

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+/- is just one of many measures of a players performance and is of more use to compare players on the same team not team to team.

The Devils' current +/- is a fairly accurate description of the quality of play from each player relative to other Devils.

T, by your own admission "We all know they are having quite a bizarre season"

Which means stats, including +/- are going to deviate from what you see typically. You should not use an anomaly as an example to make your argument. Do the same analysis for say 10 teams and I'll bet your "difference" column won't look so off.

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I don't think plus minus is stupid, just misleading at times. You really can only compare guys on the same team. But I don't get why you think SH goals shouldn't count against plus minus. Empty net goals, I agree on.

+/- is usually used to talk about how good a guy is overall defensively and offensively, combined into one number. The problem is that when a guy is on the PP he can only have his +/- hurt, since he can never get a + and can only get a -. The PK guys benefit from this, they can only positively get a + and can never get a -. So, if you're wanting to look at +/-, it's better to look at just the even strength situations because it doesn't punish players who only play PP or reward players that only play PK.

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+/- is usually used to talk about how good a guy is overall defensively and offensively, combined into one number. The problem is that when a guy is on the PP he can only have his +/- hurt, since he can never get a + and can only get a -. The PK guys benefit from this, they can only positively get a + and can never get a -. So, if you're wanting to look at +/-, it's better to look at just the even strength situations because it doesn't punish players who only play PP or reward players that only play PK.

This. Players have control over how good they are defensively, but they don't have control over their usage. That's the central problem with +/- - how a coach uses a player seriously affects his potential +/-. Kovalchuk typically plays 2 minutes of a power play and up until this year has been used sparingly on the penalty kill, plus he is almost assuredly out for all of his team's empty net situations, whereas he might not be used when his team is up by 1 or 2 late.

Kovalchuk ES +/- by year:

2007-08: -11

2008-09: -7

2009-10: +14

2010-11: -18

2011-12: -1

msweet: I haven't talked about save percentage both for and against and how little control players have over that. I agree that other teams won't look so strange.

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IDNKT!!! thanks Tri! I always thought +/- was an even strength stat it would make more sense to publish only ES +/- is there a database that keeps ES =/- numbers?

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I wouldn't call it dumb, it just doesn't tell the whole story. But shorties should count. Empty-netters, probably not.

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sure he's benefiting for his teammates and roles on the team but sykora was such a great find this season considering the cap hit...was pretty skeptical in the beginning but love him being back and contributing

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It's dumb only if you don't understand it.

I'm pretty sure Triumph understands it along with how stupid it is. Even still, it doesn't take into consideration zone starts or quality of competition.

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+/- is just one of many measures of a players performance and is of more use to compare players on the same team not team to team.

The Devils' current +/- is a fairly accurate description of the quality of play from each player relative to other Devils.

This. +/- Lets you get a better look at who is doing what on the team. Of course, like many of the other main stats, it is general and not necessarily conclusive of anything.

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Giving up so many shorties is what's stupid! Holy sh!t what a difference!!

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+/- is a silly stat... but so are pretty much every other stat in hockey. Hockey has got to be the worst sport for anyone to attempt to model statistically. The free flowing aspect of the game, the fact that there are goaltenders, and just the general lack of imposed structure to the game make meaningful statistical models of the game nearly impossible.

The worst thing about +/- is that it provides 0 predictability. A guy who has the best +/- stat in the league one year can be on the bottom of the league the next. At least with the goals stat (and, to a lesser extent, the assists stat), we can shuffle players into certain categories (in terms of things like: "this guy is a 20+ goal scorer").

Now it's time to aggravate the people on the other side of the debate though: I have yet to see any "advanced" (hockey) stats which are significantly better than the standard goals, assists, points, PIM line. Corsi and Fenwick, two of the current fads in the hockey world, suffer from problems with their construction, don't correlate well, and similar to +/- they have problems with the fact that they just don't tell you much in terms of predictions. Their better than nothing I guess, but just barely.

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I just love the way Tri sees the game of hockey itself, and can break these things down.

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Like any stat, it can be misinterpreted. Rarely can a stat looked at in a vacuum and have it tell an accurate story. Does GAA tell the whole story? No but it is one of the best we have to evaluate a goalie's performance.

Tri makes a valid point regarding the +/- of certain devils this year but I don't think it invalidates the entire stat.

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You know, +/- isn't a completely terrible stat for defensemen. For forwards is pretty much a complete crap shoot, but we all know that defensemen generate different kinds of statistics.

humm

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You know, +/- isn't a completely terrible stat for defensemen. For forwards is pretty much a complete crap shoot, but we all know that defensemen generate different kinds of statistics.

humm

What does this even mean? Anyway: http://vhockey.blogspot.com/2010/05/forest-v-trees.html

+/- is bad for defensemen for the same reason it's bad for forwards - it takes into account absolutely 0 context.

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What does this even mean? Anyway: http://vhockey.blogspot.com/2010/05/forest-v-trees.html

+/- is bad for defensemen for the same reason it's bad for forwards - it takes into account absolutely 0 context.

Good link. Thanks.

...you know, humm. I'm still reading, but as soon as I see things like: "By way of example, in 08/09 Chris Pronger had a 5v5 on-ice save percentage of .915. When he was in the game, but not on the ice, the opponents scored at a 2.20 goals per 60 clip..." it makes me start to ask questions. This is amateurish statistical thinking. But, I'll give it a chance. Be back later.

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I don't get it. This person (the author) is saying things like:

"So the correlation of 08/09 Corsi QualComp to 09/10 5v5 save percentage score is a touch stronger, r=-.09."

and we're supposed to listen to him? Has he ever taken a statistics class, even? :blink:

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