from Amazon
Tuesday, November 22, 2011
Tango’s Lab: forecasting players who switch teams
KJOK was nice enough to send me a Marcel file that includes the 2009 forecasts, the 2009 actuals, and if the player played for the same team in 2008 and 2009.
I took his data, and calculated the wOBA for each player (his forecast, and his actual). I found the weighted error as the difference between these two figures, multiplied by his actual PA.
I limited the forecasts to only those players with a reliability of at least .50, and who, naturally, played in 2009. This gave me a total of 382 hitters, with 151,897 PA.
I then simply split up the 382 players into whether they played for the same team or not. For those that played on the same team, the average error was .025. For those that switched teams, the average error was .027.
Since Marcel does not make a park adjustment, that could be a source of error. Then again, it could simply be that the change in context simply forces an error. In order to understand if park adjustment is the reason or not, we need to compare to a forecasting system that does an explicit park adjustment. (It may be that the team switchers simply are harder to forecast because there was a reason they switched teams to begin with.)
If someone has forecasts for 2009 that were made with a park adjustment, then please supply me with such a file. It MUST contain at least the following information:
bdbID, AB, H, 2B, 3B, HR, BB, HBP
If you don’t have at least exactly that, don’t send me anything!
I will then have something to compare against.