I had an interaction this morning that hurt my brain and my soul a little. It was about the difference between Plus-Minus (+/-) and Goal Differential (5v5, Even Strength, and All Situations). My takeaway from the interaction was that we still have a long way to go in dispelling the awful mythology of plus-minus.
Let us begin with the basics. If you think that +/- is the stat that tells you the difference between how many goals for and against were scored with a player on the ice, you are incorrect. That is not what +/- does, even though a lot of people think that’s what it does.
+/- is actually a mix of all kinds of things with a few caveats. It keeps track of even strength scoring for and against, but it also counts shorthanded goals for and against. In addition to that, it also counts empty net goals that are scored. So what it does is mix a whole bunch of game states together. That’s where this thing really falls apart.
The difference between Plus-Minus and Goal Differential used by anyone else in the stat community is that the nerds don’t want to cross the streams. It makes more sense for us to all know what we’re looking at when we discuss numbers. The standard game state of discussion is 5v5 play since the majority of a skater’s time is played there. It is not limited to that game state though, so when others are discussed, they are cited appropriately. For example, often the PP is broken down to even more specifically the 5v4 PP and conversely the PK to the 4v5 PK.
This way we can more clearly break down if a player is really struggling all the time, 5v5, or on one of the special teams. Empty net situations are almost never discussed because the amount of time spent playing in that state is extremely limited and under some very obviously negative conditions. If your goalie is pulled at the end of the game, it isn’t because you’re already up by three and you really want to rub it in Calgary’s face. You also aren’t likely playing the 4th line with the goalie pulled either.
When a team, like Edmonton, has been bad for the better part of a decade then those teams should have more opportunities to play with the empty net. Bad teams lose more and conversely have more situations when pulling the goalie late is a viable tactic. When they do that, good players are put on the ice in an attempt to score, but without a goalie, it’s very easy to be scored against.
For reasons that don’t make any sense, the NHL will give all of those players who were on WITHOUT A GOALIE IN THE NET a minus for that goal. The longer a quality player is employed by a bad team, the more of these minuses he will get.
The interaction that sparked this article was about Taylor Hall. I don’t want to turn this into an article about Hall though, but he is an interesting case study in +/- vs goal differential.
Over the course of his Oiler career, Taylor Hall was a -27 per the NHL’s stats page. Ignoring all context, being -27 is bad. To a lot of people, that suggests to them that Taylor Hall was poor defensively. Positive players are good. Negative players are bad. Makes perfect sense. Right?
However, when it comes to 5v5 goal differential, Taylor Hall was +3 as an Oiler. When it comes to All Situations goal differential, Taylor Hall was +92 as an Oiler. In his Oiler career, the club scored 426 goals for and had 334 scored against with him on the ice. The Oilers only scored 686 for and had 1074 against with him on the bench (all situations) for a -388 goal differential.
Still, +/- tells you that Hall was a negative player. It has to do with the fact that with 6 skaters on the ice (goalie pulled), the Oilers had only 21 goals for but 57 goals against during his time as an Oiler. That is a -36 being applied to a bunch of players who the coach trusted to play without a goalie because they needed a goal. If you want to know how Taylor Hall ended up with a -27 as an Oiler, this game state is the culprit.
For a non-Oiler example, let’s look at Jack Eichel. Since coming into the NHL Jack Eichel has been playing for the Sabres, who are Oilers-East but without the lottery wins. In just 2.5 seasons Eichel is a combined -45 in Buffalo. It’s ugly.
In 5v5 goal differential, Eichel is actually -22 in that time. That’s half the negative that +/- reports! In all situations, he is +25 in goal differential (thank you, Power Play). The Sabres have scored 208 goals and had 183 scored against with him on the ice. They have scored 102 goals and 210 against with him on the bench for a -108 differential.
The difference between -22 5v5 and -45 by +/- standards is still a lot. What’s going on there? Well, in just 2.5 seasons the Sabres have a -22 goal differential with the goalie pulled. We can be pretty sure that Eichel is on the ice for the majority of the time the goalie is pulled.
What about Connor? Deep down, everything is about Connor.
Since he joined the NHL, Connor McDavid is +35 (highest among Oiler players). But even he is getting short-changed! 5v5 McDavid has a +39 goal differential. In All Situations, he has a +74 goal differential. Connor McDavid is offensive potential in human form and that ridiculous empty net/shorthanded goal portion of +/- is even affecting him.
We can run this exercise for every good player on bad teams in the NHL and you’ll see the same thing over and over again. Goal differential is a very coarse measure because goals happen pretty infrequently, but if we start mixing and matching game states like +/- then we lose the ability to be certain about the things *we think* we know about players.
For me, if I want to get closest to the spirit of what most people think they’re getting from looking at +/- then I go to 5v5 goal differential. There are no special teams. The game isn’t being played under really strange conditions. It’s hockey as we know it. I am happy that we have tools available to us that let us get much more precise than +/- ever can. We can break things down really quickly and be able to say more with more confidence because of it.
So please don’t ever use plus-minus. Ever. It’s hot garbage. We can do better. It’s 2018.
*stats courtesy of Corsica.Hockey