THE BOOK--Playing The Percentages In Baseball

Tuesday, November 27, 2007

PITCHf/x data quality

Mike Fast reports on more data quality issues:

...Chamberlain throws Lind five straight sliders to strike him out and end the inning. Unfortunately, however, the pitch locations recorded by PITCHf/x for these pitches were mistakenly attached to the wrong pitches in the Gameday XML data.... Then the order of the other pitches is out of whack, too. The pitch labeled #1 should be #5, #2 should be #1, #4 should be #2, and #5 should be #3.

I don’t intend my notation of this example in any way to disparage the incredible work that MLBAM and Sportvision have done in creating this data set and making it available to us. For free, no less. It’s an incredibly valuable resource, and some errors are to be expected during a season in which the system was being evaluated and debugged.

I just don’t know how prevalent these kinds of errors are and when they might call into question some of my conclusions. I do know that Eric Van spotted a similar error in Josh Beckett’s data from Game 1 of the division series, as detailed in this thread at Sons of Sam Horn, post #88. The PITCHf/x data in question for that game has since been removed from the data set altogether. 

As long as you get a substantial % correct in the aggregate, that should satisfy most research needs.  Just something to keep in mind, when looking at the data on an individual basis.  And Mike is right that it’s not everyday that we get the luxury of seeing Beta results in a production environment for the general public to consume.