[M T]

A statistical analysis is hard because one player’s +/- is dependent on both who else is on the court and who the opponent is.  It is a crude measurement, but does tell you a bit on how the team does when a particular player is on the floor.

The same can be said of most any other statistic (FT% is the only exception I can think of).  Just take scoring.  If a 6' player plays against 5' players, doesn't that affect the person's scoring?  If a player angers the PG and never sees the ball, doesn't that affect the person's scoring?   When an opponent face-guards Jump the entire game, doesn't that affect her scoring, and also the scoring of her teammates?  And, there are more confounding factors.  What if Missy is a ref? 

Something like EFF is crude because it includes only a handful of other statistics that are only indirectly associated to the outcome of the game.   It clearly gives higher values for certain positions on the court, so at best it is useful for comparing two people in the same position on teams that run similar offenses. 

The team can score 98 points and lose a game, or score only 54 points and win a championship.

If you tell me the sum of the +/- for all the players on the team in a game, I can tell you not only whether they won or not, but also how much they won (or lost) by.

And, like most stats, the raw number isn't meaningful without knowing the playing time.

[M T]

A statistical analysis is hard because one player’s +/- is dependent on both who else is on the court and who the opponent is.  It is a crude measurement, but does tell you a bit on how the team does when a particular player is on the floor.

The same can be said of most any other statistic (FT% is the only exception I can think of).  Just take scoring.  If a 6' player plays against 5' players, doesn't that affect the person's scoring?  If a player angers the PG and never sees the ball, doesn't that affect the person's scoring?   When an opponent face-guards Jump the entire game, doesn't that affect her scoring, and also the scoring of her teammates?  And, there are more confounding factors.  What if Missy is a ref? 

Something like EFF is crude because it includes only a handful of other statistics that are only indirectly associated to the outcome of the game.   It clearly gives higher values for certain positions on the court, so at best it is useful for comparing two people in the same position on teams that run similar offenses. 

The team can score 98 points and lose a game, or score only 54 points and win a championship.

If you tell me the sum of the +/- for all the players on the team in a game, I can tell you not only whether they won or not, but also how much they won (or lost) by.

And, like most stats, the raw number isn't meaningful without knowing the playing time.