You can find part 1 here where we covered some more specific examples and comparisons of why the +/- statistic holds very little relevance in the game. In this post we will cover many of the flaws in the general make-up of the +/- statistic that diminishes its validity.
First a quick recap of how exactly the +/- statistic is defined:
- + When a player is on the ice and their team scores at even strength, they receive a +1
- + When a player is on the ice and their team scores short-handed, they receive a +1
- - When a player is on the ice for an even strength goal against, they receive a -1
- - When a player is on the ice for a shorthanded goal against, they receive a -1
- When a power play goal is scored, none of the players on the ice receive a + or a -
- Penalty shot goals are not counted into +/-
What is the common perception of what +/- gauges?
People often view +/- statistic as an all encapsulating statistic to gauge how effective a player is on the ice. Basically this player is responsible for this many goals for while on the ice and responsible for this many goals against while on the ice. If the number is positive then the player is playing well and is positively affecting the team, if the number is negative then the player is not playing well and is negatively affecting the team. This is the crux of the argument for those arguing Regehr is not having a good year and those saying Gragnani isn't playing that poorly because he is +10. There are many inherent flaws with this view-point and this statistic in general.
Inherent Flaws
There are six players (including the goalie) on the ice at any given time, all it takes is for one player to make a mistake for a goal to be scored. Conversely, all it takes is one great effort by a single player to score a goal for.
For example, say the opposition comes down the ice on a rush only to realize that Buffalo has every angle covered. The player pulls up at the blue line to allow his teammates to gain the zone, then he fires a shot on net from 50 feet to create a rebound but the shot somehow eludes Miller. The goal was a result of a mistake by Ryan Miller but now the five players on the ice that covered the defensive zone so well forcing the shot to be taken from 50 feet out are all pegged with a -1. Numerically, this indicates that everybody on the ice executed poorly when in reality, everybody did exactly as they were supposed to.
Also, there is a lot of luck involved in this statistic. Luck, in terms of the +/- statistic, would be defined as a bad bounce or a well timed shift change. For example, about a month ago, Brayden McNabb faced an odd man rush coming his way and was able to break the play up in textbook fashion. In the process, his stick was broken, so he dropped his stick and continued fighting for the puck and then kicked it up to a forward streaking the other way. McNabb then hustled to the bench for a line change, seconds after McNabb stepped off the ice and Gragnani stepped on, the Sabres scored off the rush that McNabb created by stopping a goal against and working hard to get the puck to his forward. +1 for Gragnani and McNabb has nothing to show for it. This type of play happens quite often for defenseman as an odd-man rush the other way is a convenient time for defensemen to change at the end of a shift.
Conversely, the opposite happens a lot of times for forwards. Say there is what appears to be a non-threatening rush heading the other way so a forward heads off to catch a breather. In the meantime, the man that player was supposed to cover sneaks up into the play now creating an odd man rush and that team scores, just after the guilty player steps off the ice. So now this one player coming off the bench didn't even have time to take three strides and now he's saddled with a -1. In addition, the four other players who did what they were supposed to and had the play covered, are now all saddled with a -1 as well.
Quality of Linemates/Team
Somewhat related to the preceding point, is the relevance of the quality of linemates in +/-.
Comparing players' +/- across different teams is utterly baffling to me, yet it is still done on a consistent basis. Ian White and Johnny Boychuk are 3rd and 7th in the league in +/-, does that imply they are two of the top three (Chara sandwiched in between these two) defensemen in the league? Or does it mean they have the benefit of playing on very good teams? Or being paired with great defense partners in Chara and Lidstrom? You can argue that you can compare two players that are both on very good teams as they are both on an even playing field. The Red Wings are only one point ahead of the Rangers, does that mean Michael Del Zotto is the Eastern Conference equivalent of Nicklas Lidstrom (both +22)? +/- is largely a function of the team you play on rather than the play of an individual player. The Del Zotto/Lidstrom case will be covered in the next section as well.
As mentioned previously, all it takes is a mistake from one player on the ice for a goal to be scored. If you are consistently paired with a player who makes frequent defensive mistakes, NHL players will capitalize on that on a regular basis, and the +/- statistic penalizes you for that.
Quality of Competition
Take into consideration a defensive defenseman like Robyn Regehr. His sole purpose on the ice is goal prevention, he is not expected to generate offense and very little offense will come with his ice-time. Regehr will face the best that the other team has to offer on a nightly basis: Crosby, Malkin, Giroux, Stamkos, Richards, Datsyuk, etc. These types of superstars face top defensive pairings on a nightly basis as well, yet they still produce offense. The bottom line is that these guys are going to score on you, no matter how good you are defensively. This loosely ties in with the preceding point as well, you may be up to the task of defending a Pavel Datsyuk but if the other four guys on the ice are not, he will exploit that and score on you.
Shutdown defensemen are inherently at a disadvantage when it comes to +/- as they will face top assignments on a nightly basis while generating very little offense. If Robyn Regehr had the offensive game of a Shea Weber, I can promise you it would've taken more than a mid-range prospect and a bottom pairing defenseman to trade for him. Guys like him are brought in purely for defensive purposes and his +/- will suffer as a result of that. It cannot be stated enough that his negative +/- does NOT imply that he's not helping the team. Throw Marc-Gragnani or Mike Weber out against Datsyuk, Malkin, etc on a nightly basis and see how the team fares. The Del Zotto/Lidstrom example is another example of the quality of competition affecting a players' +/-. Lidstrom can play at both ends but he also often faces the opponents' best lines, putting him at an inherent disadvantage when comparing his +/- to somebody like Del Zotto who faces a little easier defensive assignments.
Being a shutdown defenseman is a dirty, thankless job but one that is necessary on any successful team.
Conclusion
There are many advanced statistics now that should eventually replace +/- in coming years. Corsi numbers essentially increases the sample size quite drastically, thus reducing luck. There are quality of competition and quality of teammate metrics that can be used along with +/- to potentially better evaluate a players effectiveness. GVT is another relevant statistic that essentially measures what a players value is, in goals, over a replacement player. As it stands now, there are far too many exterior variables and far too much luck that plays into +/- to make it a relevant statistic in today's game.
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