Earlier this month ESPN unveiled a new advanced basketball metric called “real plus-minus” (RPM). The statistic was developed by Jeremias Engelmann and is trumpeted as an improvement over its predecessors, adjusted plus-minus and real adjusted plus-minus. One of the unique features of RPM is that it splits a player’s impact into offensive RPM (ORPM) and defensive RPM (DRPM). While ESPN has yet to unveil the exact methodology for RPM, early reactions to the stat can be read here, here and here. According to ESPN:
“RPM estimates how many points each player adds or subtracts, on average, to his team’s net scoring margin for each 100 possessions played. The RPM model also yields separate ratings for the player’s impact on both ends of the court: offensive RPM (ORPM) and defensive RPM (DRPM).”
Naturally, we were interested in visualizing the relationship between RPM and NBA salaries. With the exception of a few notable outliers (Stoudemire and Boozer), we found a strong relationship between RPM and annual salary. Once you take into account players who signed large contracts before suffering serious injuries (Stoudemire) and players on the end of lengthy contracts whose skills may have deteriorated (Pau Gasol), on average NBA teams appear to reward higher RPMs with higher salaries. However, as you’ll see in this first graphic there are a lot of players who fall well-below or well-above the line of best fit.
To understand what’s happening here we have to unpack RPM into its offensive and defensive components. The bottom line may not come as a surprise. From a salary perspective, offense trumps defense, by a lot. Merging ESPN’s RPM data with salary information from Basketball-Reference, we estimate that an additional point in ORPM is worth on average $1.4M extra a year in salary while an additional point in DRPM only earns an $700K on average. This makes defense a bargain when you consider that a point scored should be equivalent to a point prevented.
The results are even more striking when we control for position. In essence, we’re now asking for the average relationship between salary and RPM within position. Using the same specification but now with controls for position, we find that a point in ORPM is still valuable at $1.5M (and highly statistically significant) while a point in DRPM falls to $300K (and is no longer statistically significant). To reiterate this, if we compare two players at the same position we find that difference in their salaries is heavily driven by their production on the offensive end and has no connection to their defensive impact. For those who have argued that defense is under-rewarded in the NBA, this may not be a smoking gun, but it is notable.
We can also rank players in the NBA according to value by constructing their predicted salary based on ORPM, DRPM, position and tenure and comparing this to their actual salaries. To be conservative, we dropped anyone who played fewer than 50 games this season. Below is a list of the top and bottom five players by value in three categories: guards, forwards and centers.
Top 5 Players by Position
|Vince Carter||$6,422,378||Nick Collison||$11,015,718||Audray Blatche||$8,663,985|
|Ray Allen||$5,464,209||Chris Andersen||$9,654,286||Ryan Hollins||$6,032,525|
|Goran Dragic||$5,185,118||Mike Miller||$8,263,340||Nazr Mohammed||$5,131,789|
|Derek Fisher||$4,658,847||Matt Barnes||$7,520,160||Alexis Ajinca||$4,917,366|
|Kyle Lowry||$4,465,802||Matt Bonner||$7,254,578||BeJuan Blair||$4,725,142|
Bottom 5 Players by Position
|Joe Johnson||-$13,011,606||Amare Stoudemire||-$18,847,008||Dwight Howard||-$10,757,813|
|Dwyane Wade||-$12,158,871||Carlos Boozer||-$12,417,897||Pau Gasol||-$9,139,959|
|Deron Williams||-$8,344,061||Rudy Gay||-$11,260,331||Chris Bosh||-$9,090,025|
|Eric Gordon||-$7,023,669||Carmelo Anthony||-$10,155,075||DeMarcus Cousins||-$7,399,312|
|John Wall||-$6,838,249||Blake Griffin||-$8,622,789||Roy Hibbert||-$5,980,450|
We’ll post links to the full lists by position shortly.