I'm not sure how thats a bias.
I came up with the player performance adjustments after several people pointed out (correctly) that the raw +/- treated each guy in the lineup the same, whether he was playing well or not - as measured by things like rebounds, assists, shots made and all the "normal" measures of contributions.
So one issue could be in how various contributions are weighted (rebound versus steal or assist or whatever).
Another potential issue is the assumption that the team has freedom in shot selection - that a guy who goes 2 for 4 from the field is equally as effective as a guy who goes 4 for 8 - in other words there's no credit for taking a shot.
Well the issue with +\- in general it doesn’t account for who the player is on the court with as well as who they are playing. It shows a bias to someone who plays against worse competition and/or has better teammates on the floor with them. If you’re on the floor for a good run… say a teammate gets hot and hits 2-3 three’s in a row and lay up. Did you really make those plus plays?
Plus and minus is more geared to lineups instead of individual players. It’s still not perfect as it doesn’t measure competition. There’s also not a whole lot of data points throughout a season.
The adjustments come into issue for in that there’s a lot of + and - plays that don’t show up on the stat sheet and/or show up on someone else’s stat sheet even though someone else made the play.
Ex. 1 Player A gets hand on a missed shot and tips it out to someone who actually secures the rebound and logs the rebound stat. Both players netted a plus play
Ex. 2 Player A tips a pass, or strips a ball and Player B secures it. Player B gets the steal but player A created the plus defensive play.
Ex. 3 Player A makes a bad read and passes the ball that puts player b in bad position resulting in a turnover. Player A made the - play and but Player B is penalized on the the stat sheet.
Ex. 4 Player A drives the ball sucking in the defense and kicks the ball out player B who makes the extra pass to player C who hits their shot. Player A initiated that whole sequence and they all deserve a plus play as that’s good basketball but only player c and b get credit.
Ex. 5 Player A sets a solid screen and/or shields the help defender from collapsing and player B scores. Player B gets an adjustment for points scored and Player A gets penalized for making a plus play.
Ex.6 Player A walls up and stops an opposing play from getting good position Player B comes behind and blocks the shot 1-3 times and the backboard gets it 0-2 times. Player B gets an adjustment for the block but both make a plus play.
Correct me if I’m wrong but don’t your adjustments add to the player who recorded the stat and subtract from the rest of the players on the court (turnovers the inverse is true)?
A player who plays extremely solid defense and then moves the ball well and sets screens is at a major disadvantage in this stat. They could set all the right screens, make cuts that free up space, make excellent passes that don’t result in assists for them but either causes a favorable matchup for a teammate or results in assist for a different teammate and it wouldn’t show up as much in their personal +\- . The adjusts would in-fact hurt the player even though they are constantly making + plays.
Your adjusted +\- has a bias to stat sheet stuffers. That’s fine and idk how you’d eliminate that outside of watching tape and designating plus play and minus play but that would add human bias.
All stats have a bias. The important part is to understand the context of the stats with that bias. Acknowledging the short comings of a stat while also not misleading people by providing context to it.
