Plus/minus

Plus-minus is a statistic that measures the team goal differential when a specific player is on the ice. Players' plus-minus stats get increased by one every time their team scores an even strength or shorthanded goal while they are on the ice. Their plus-minus is decreased by one every time their team allows an even strength or shorthanded goal while they are on the ice (whether or not the net is empty does not matter for purposes of plus-minus). The plus-minus is never affected when a power play goal is scored by either team.

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. For example, a skilled player could be placed on a line with other, less skilled players which may cause his/her plus-minus to be lower than usual even though the player's individual performance may be just as good as before (or perhaps even better).

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 the defensive performances of the team as a whole.

History
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 ratings 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 Plus/Minus Award has been awarded to the NHL player with the highest plus-minus at the end of the regular season; since they log more even-strength ice time, the winners tend to be defensemen. 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 Chris Pronger twice. 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. In the 2002–03 season Peter Forsberg and Milan Hejduk were both +52 for the season as members of a high-powered line with Alex Tanguay. Forsberg led the league in points (106) and Hedjuk in goals (50) on the way to their shared +/- title that year.

The NHL single game plus minus record is +10 held by Tom Bladon on Dec 11, 1977.

Notables
Top 3: Season high
 * Bobby Orr, 1970–71, (+124)
 * Larry Robinson, 1976–77, (+120)
 * Wayne Gretzky, 1984–85, (+98)

Top 5: Career high
 * Larry Robinson, career, (+730)
 * Bobby Orr, career, (+597)
 * Ray Bourque, career, (+528)
 * Wayne Gretzky, career, (+518)
 * Bobby Clarke, career, (+506)

Top 3: Season low
 * Bill Mikkelson, 1974–75, (-82)
 * Jack Lynch, 1974–75, (-69)
 * Greg Joly, 1974–75, (-68)