R: Baseball Pitching Wins Above Replacement and Salary


Are elite baseball pitchers worth their salaries? To investigate this I fitted linear and robust linear models using Baseball-Reference.com definition of wins above replacement. The universe of data is all pitchers in the year 2015 who started at least 20 games or as a reliever pitched 70 outs which is 298 players.

The distribution of war is below:

 Min.      1st Qu. Median Mean    3rd Qu. Max.
-1.79      0.2125  0.95      1.219   1.905     9.28

standard dev: 1.61
mad:  1.245

Distribution of Pitching WAR
























Fitting a linear model to the data:







We can see that there is a linear relationship between salary and war as salary is significant.  The correlation between the two variables is ~.28 but the MSE is 2.4 which indicates the model isn't the best fit.  The linear model suggests that each additional $11,883,599 in player salary should buy a win over a replacement player.



























Investigating a robust model:


















The robust model is a better fit as MSE is significantly lower at 1.47.  The correlation between salary and war is slightly lower at .277.  The advantage of a robust model is it will minimize outliers by assigning lower weights.  The robust model suggests that each additional $14,065,063 in player salary should buy a win over a replacement player.



Below is a table of 2015 war, 2015 salary, and the upper prediction interval of war based on 2015 salary:




































The top ten pitchers in 2015 all had better seasons than the upper end of the prediction interval based on their salary. 

No comments:

Post a Comment