REAL PLUS MINUS:
A metric provided by former Phoenix Suns consultants Steve Ilardi and Jeremias Engelmann, based on Engelmann's version (xRAPM) of
Regularized Adjusted Plus-Minus
Real Plus Minus is the player's average impact in terms of "net point differential" per 100 offensive and defensive possessions. RPM can be broken down to offensive and defensive metrics:
Offensive Real Plus Minus: (ORPM) Player's average impact on his team's offensive performance, by the points scored per 100 offensive possessions
Defensive Real Plus Minus: (DRPM: Player's average impact on his team's defensive performance, by the points allowed per 100 offensive possessions.
What Adjusted Plus-Minus does:
It reflects the
impact of each player on his team's scoring margin after controlling for the strength of every teammate and every opponent during each minute he's on the court.
What Adjusted Plus-Minus incorporates:
Every time segment a player is in a game, adjusted plus-minus tracks:
(1) The other nine players on the floor,
(2) The length of the segment,
(3) The score at the start and at the end of the segment.
What are the PROs and CONs for Adjusted Plus-Minus?
PROS:
The biggest advantage of adjusted plus/minus ratings are that they are one of the the closest we can come to an unbiased measure of a player's effectiveness.
CONS:
(1) Adjusted plus/minus ratings are have a high variance. The regression tries to find a constant value for a player, but this value can change pretty dramatically with a different role, a different coaching scheme, different teammates, or different match-ups.
(2) There is noise in the data. For some players, especially when only looking at data over just 1 year, there are some strange results, but that is to be expected. An examination of 239 players revealed that only 7% of the variation in a player’s adjusted plus–minus value in 2008-09 was explained by what he did in 2007-08. Although more data does increase the level of statistical significance, it’s still the case that most players even when five years of data is employed are not found by this method to have a statistically significant impact.
(3) Another issue which adjusted plus-minus technique struggles to address is the
multicollinearity issue. Coaches prefer to use some player duos/trios frequenly or rarely since all players could not be on the court with every other teammate at the same time.