The statistic can be frustrating for its randomness: players receive a plus when they’re on the ice for an even-strength or short-handed goal for and a minus when they’re on the ice for an even-strength or short-handed goal by their opponent.
A player may receive credit despite contributing little to a goal or be penalized with a “dash” even if he wasn’t responsible for his team giving up a goal. And yet, players, coaches and managers still rely on it to measure effectiveness.
“I get upset about it because I know that everyone else uses it as a gauge,” said Krug, who has a plus-11 mark this season. “And being an offensive defenceman people are like ‘Well he’s plus-5, but everyone else on his team is plus-25, he obviously can’t play defence’. So that just bothers me.”
Consider his recent minus-3 performance against Florida, during which Krug was dinged once for a short-handed goal against and again later for an empty-netter. Neither play, in his mind, deserved any kind of statistical penalty.
"Personally I hate it," Krug said of the plus/minus rating. "I pay attention to it because people use it as a gauge for how many goals you're on for and against, (but) I think it's misleading to show how many goals you're out there contributing to your team."
The 24-year-old thinks he's been hit with a minus on at least seven empty-net goals. Many players feel such a penalty should, at the very least, be adjusted in the plus/minus rating.
"Those are devastating to your plus/minus," Maple Leafs centre Nazem Kadri said, "especially when you're falling behind in games like we were early on in the year."
Kadri has been on the ice for eight of the 11 empty-net goals Toronto has allowed this season, which skews his ugly-looking minus-14 rating entering Monday's play. Even if it's misleading, Kadri knows the statistic is used by coaches and acknowledges that goal differential is "huge" in terms of trusting players and knowing who to put on the ice.
Kadri can at least take comfort in the fact that Leafs head coach Mike Babcock subtracts empty-net goals from his plus/minus tally.
"Because sometimes you get screwed for being a good player," Babcock said. "So I take it right out of the mix and then I add up and I see where they're at."
Babcock analyzes five-game reports on who's plus and who's not. He also looks at points, penalty minutes and reports from the Leafs analytics staff for further assessment. A tally of scoring chances for and against is a better nightly measurement of which players played well and which didn't, Babcock says.
Even while acknowledging the randomness of the stat, Babcock seems to value it as one spice in the larger recipe of evaluation.
The former Detroit Red Wings head coach points to Nicklas Lidstrom, who ranks 10th all-time with a plus-450 career rating. That mark is not by accident, according to Babcock.
While easily one of the best defencemen ever, Lidstrom also played for some terrific teams in Detroit, a factor that affects the plus/minus rating. Players on better teams are likely to score more goals than their opponents and thus boast more pluses.
"So how come some guys are on a good team and got 100 points and are minus?" Babcock said.
Boasting an even rating this season, Lindholm basically ignores his nightly plus/minus when evaluating his own play, pointing out that the statistic heavily depends on random events outside one player's control, such as matchups and the performance of teammates.
It's difficult to pinpoint what the rating actually demonstrates. Penguins winger Chris Kunitz, for instance, has a substantially better rating (plus-31) than Sidney Crosby (plus-16), whose worth to Pittsburgh obviously far outweighs that of his elder teammate.
Indicative of its randomness, the rating tends to fluctuate year to year even for some of the game's elite. Among the NHL leaders in plus/minus this season, Kings centre Anze Kopitar held a minus-2 mark last year.
Players know it carries weight with coaches and managers, to the point that those in the minors are known to stay on the ice just a tad longer if they smell a goal and subsequent plus coming.
The rating systems seems likely to lose more value as deeper evaluation through analytics becomes an even larger part of the game, much as batting average lost worth in baseball with the rise of on-base percentage. Puck possession, which measures many more events throughout a game, is viewed as an infinitely better indicator of ability.
"I think we're kind of creeping that way because there's so many more analytics that are kind of creeping their way in," Krug said. "I don't even know what any of the crap is, Corsi or stuff like that...(but) I think eventually it's going to overtake just a simple plus/minus, if you're on the ice, if you're not.
"I think eventually we'll probably get away from it."