Plus–minus (+/−) is an ice hockey statistic that measures a player's goal differential. With the exclusion of penalty shot goals, when an even-strength or shorthanded goal is scored, the plus–minus statistic is increased by one ("plus") for those players on the ice for the team scoring the goal; the plus–minus statistic is decreased by one ("minus") for those players on the ice for the team allowing the goal.[1] The plus–minus statistic is not affected by power play goals. Also, whether or not the net is empty does not matter for purposes of plus–minus.
The statistic is sometimes called the plus–minus ratio even though it is a difference, not a ratio. It is also sometimes referred to as plus–minus rating although this is inaccurate as well.
A player's plus–minus statistic can be calculated for a single game or for the season as a whole. For instance, if a player enters a game with a season total plus–minus of −8, then accumulates a statistic of +3 for a single game, the season total will change to a −5.
Plus–minus is mainly used to measure defenders and forwards who play a defensive role since offensive forwards are better measured by scoring statistics such as goals and assists. It is directly affected by team performance, thus accurate comparisons can only be made by taking into consideration both the offensive and defensive performance of the team as a whole.
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The Montreal Canadiens were the first team to track +/-, starting sometime in the 1950s. Other teams followed in the early 1960s, and the National Hockey League (NHL) started officially compiling the statistic in 1968. Emile Francis is often credited with devising the system, but he only popularized and adapted the system in use by the Canadiens.
Since 1983, the NHL has awarded the NHL Plus-Minus Award each year to the player with the best (highest) plus-minus statistic during the regular season. Defencemen tend to win the award more often than forwards, since they log more even-strength ice time.
Similarly,the Western Hockey League (WHL) awards the WHL Plus-Minus Award each year to one of its players.
The most prominent plus-minus winner was Boston Bruins' defenseman Bobby Orr, who led the league six times (and whose defence partner Dallas Smith was the first league leader). Wayne Gretzky led the league four times and the only other players to lead more than once are two-time leaders John LeClair and Chris Pronger. Larry Robinson, the career leader in plus-minus, only led the league once. Ray Bourque, third on the all-time leaderboard, never led the league in plus-minus for a single season.
The NHL single game plus minus record is +10 held by Tom Bladon on Dec 11, 1977.
The following statistics are since the 1968-69 NHL season, when plus-minus became an official statistic.[2]
Top 3: Season high
Top 5: Career high
Top 3: Season low
Although the statistic was pioneered in the sport of hockey, it has found its way into use in other sports and areas of life. For instance, the NBA's Houston Rockets first utilized a modified version of the stat, which helped reveal the unheralded effectiveness of light-scoring Shane Battier.[3] It is now in regular use throughout the NBA.
The plus-minus statistic has also found its way into the classroom, being used by law school deans to identify effective professors.[4]