NBA Plus-Minus (+/-) & Player Impact Metrics


NBA Plus-Minus, a.k.a. +/-, simply keeps track of the net changes in the score when a given player is either on or off the court. The NBA has been publishing plus-minus values in official box scores since the 2007-2008 season. A variety of combinations including the best two-player, three-player unit, and even five-player combinations for each game can be provided with the plus-minus technique.

Plus-Minus Calculation
Plus-Minus for Any Player=(Team Points Scored While That Player is On The Court) – (Team Points Allowed While That Player is On The Court)

Relying solely on plus-minus is a huge mistake so, some analytical minds have developed and tried to reduce the +/- flaws in an effort to get more accurate results regarding a player’s impact. Currently, different types of plus-minus metrics are being published and here’s a collection:

The Good Thing About NBA Plus/Minus

The main advantage of plus/minus statistics is that they account for a player’s contributions that the box score does not keep an eye on. Setting effective picks, spreading the floor, and playing solid help defense are all instances of talents accounted for by plus/minus statistics that individual player statistics do not convey.

The Bad Thing About NBA Plus/Minus

Plus/minus statistics measure how a team performs while a certain player is on the court, and are thus the individual player equivalent of the team efficiency differential (offensive rating minus defensive rating).┬áMost plus/minus statistics have the problem of confounding a player’s performance with the performance of his four teammates (and five opponents) while on the court. Net plus/minus statistics correct for some of this problem by deducting how the team performs without the player, implying that player substitutions are uncorrelated. However, net plus/minus statistics do not account for strong correlations between teammates’ minutes on the court and systematic differences in the quality of opponents various players face. Starting lineups, as well as deep reserves, frequently play a substantial number of minutes together. The coefficients on the player variables isolate the marginal contributions of particular players while accounting for teammates’ and opponents’ contributions. However, in general, obtaining reasonably precise estimates for these coefficients requires a large number of games.

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