Substitution Effect on Plus-Minus Statistics in FIBA Competitions
Study co-authored with Topi Halme.
The plus-minus statistic measures a basketball player's contribution on the court by counting the net points scored by the two teams while the player is on the court. According to the FIBA Statisticians' Manual, the lineups on the court are updated before calculating the plus-minus statistics when substitutions take place between a shooting foul and the ensuing free throws. For the defensive team, this benefits those players who are substituted out and penalizes those who are substituted into the game. Based on the data collected from Finnish Korisliiga over the seasons 2018-19 through 2023-24, this ''substitution effect'' adds unnecessary noise to already volatile plus-minus statistics and the standard deviation of this noise is approximately 11% of the standard deviation of the corrected plus-minus statistics. The substitution effect is positively correlated with individual players' tendency to commit shooting fouls and this correlation is statistically significant. In other words, the current method for calculating plus-minus values does not measure the players contribution properly and it could be improved by handling the substitutions only after the net points from the free throws are added to the players’ plus-minus tally.
