Differential person functioning applied to baseball.

The question of whether a baseball player generally hits better against a left-handed or right-handed pitcher is difficult to answer since handedness is only one of many possible attributes of pitchers. The concept of differential functioning from psychometrics is applied, considering both the effect of the handedness of the pitcher and his earned run average (the mean number of runs scored against a pitcher per 9 innings pitched excluding runs due to errors). Two interesting cases are examined, a left-handed batter and a switch-hitter.