History of Versions
Since the inception of Value Add was announced on www.crackedsidewalks.com in 2011 and then to a national audience through Sports Illustrated, several updates have been issued. This blog intends to give a basic overview of the system. At the highest level, there are three factors that go into determining a player's value;
1) How many fewer points would a team likely average if the player in question missed a game (we do not give any player a negative rating even if his offense is worse than a typical replacement player, he just gets a 0.00). This number is the individual equivalent of the AdjO team rating at www.kenpom.com.
2) How many more points would an opponent likely score if the same player was missing from a game (on defense, the player wants a negative rating but can get a positive rating if poor defense allows more points). This number is the individual equivalent of the AdjD team rating at www.kenpom.com, and if you subtract this number from the AdjO in #1 above, you get the individual equivalent of the AdjEM team rating on www.kenpom.com.
3) What adjustments do you need to make to that figure to account for the comparison to what a replacement player would give you playing the same position (PG, SG, SF, PF or C), for the fewer possessions a player will get playing on a great team that often rests players in blowout wins, and to adjust this figure to a points per game total that is more easily understandable by fans and corresponds to the point total of each team as calculated by Sagarin's Basketball Rankings.
As outlined in the first paragraph, a player must miss a game, you subtract AdjO, AdjD and AdjEM from the team's ratings at Pomeroy, and you subtract his Value Add Version 5.0 Pts/Game from his Sagarin total to estimate the team's ratings if he were not there.
To be even more precise, the actual impact on the team's margin of victory or defeat is equal to the player's Value Add Pts/Gm MINUS that same total for the seventh best player on the team, meaning the impact of losing a 7th, 8th or 9th player on a team is usually not work any adjustment.
Here is an outline of the version of Value Add Basketball since it's public introduction in 2011.
Value Add Basketball 1.0
Value Add 1.0 was released in My of 2011, constructive critics like Basketball Prospectus took a good look at some tweaks they would make to the system. Some tweaks were made over the course of three years, but we did not formally note a Version 1.1, 1.2, 1.3 etc.