paulbball wrote:
Take plus minus from boxscore and adjust it.
We need to do adjustment because teams are not equal. Most GSW players have amazing plus minus. The pros of a plus minus based stat is that they are largely an unbiased measure of a player's effectiveness. Who cares what kind of numbers you put up or don't put up as long as your team is +20 pts per 100 possession with you playing.
APM: you take the basic plus/minus that you see on boxscores, solve a system of linear equations that takes into account the teammates and opponents on the court. Why? See above sentence. It doesn't do a good job at doing this because basketball is not a 1v1 game.
The obvious idea is:
-- Assume everybody has a "true" +/- score.
-- Take every unique collection of 10 guys on the court, look at the actual +/-, and use that as an estimate of the overall sum/difference of the 10 guys' true stats.
-- Fit this data with the best estimates for "true +/-" you mathematically can.
Weighting all that for minutes played would be straightforward. Weighting it for various late-game/end-of-quarter tactics is less so, but such flaws are shared by almost all statistical approaches, so let's ignore it.
Why doesn't that work?
Banned temporarily for, among other sins, being "Extremely Deviant".