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February 25, 2008

Schrodinger's Bat

What Would Bacon Do?

by Dan Fox

"It is the peculiar and perpetual error of the human understanding to be more moved and excited by affirmatives than by negatives."
--Francis Bacon (1561-1626)

Since everyone else seems to be chiming in on the fielding prowess of Derek Jeter, perhaps it's relevant to pause and ask the question, what would Sir Francis Bacon, the English philosopher and statesman, have thought of Jeter's defense? That question may be more relevant than it would first appear since not only did Bacon popularize what we now call the scientific or Baconian method, but he also, in his wildly ambitious quest to categorize all of human knowledge in a 1620 book called Novum Organum (meaning 'New Instrument'). In it, he classified intellectual fallacies into what has been called "the four idols." Both his method and Novum Organum have a bearing on the question of Jeter's ability at shortstop.

First, of course, there is the question of whether one can objectively evaluate Jeter's defensive ability, or that of any shortstop. The question of defensive analysis has been a stickler for most of major league history due primarily to the lack of creativity in determining what to track; the same six official fielding stats—games played, total chances, putouts, assists, errors, and fielding percentage—adopted by the National League in 1876 are the same six in use more than 100 years later. However, the ease with which new kinds of data can be collected and analyzed in recent years has made the task far easier.

Building off of a wealth of new data that includes play-by-play records of each and every of the almost 200,000 events in a major league season complete with observational recording of each batted ball and its location on the field, researchers have constructed sophisticated systems (although based on straightforward and accessible ideas) that probabilistically debit and credit fielders for making or not making plays judged as similarly difficult, as compared to their peers.

University of Pennsylvania professor Shane Jensen's Spatial Aggregate Fielding Evaluation system (SAFE) has certainly grabbed the attention of the media after he revealed at a meeting of the American Association for the Advancement of Science in Boston that Jeter ranks at the bottom of the list of shortstops in the 2002-2005 period, averaging nearly -14 runs per season. Only Michael Young of the Rangers was even close, at -13 runs. But Jensen's system is only one of several built on similar principles, all of which rank Jeter poorly, and some of which are shown in the following table. A quick confession: while also relying on play-by-play data, SFR does not use as fine-grained data as the other systems, but I place it hear alongside these other metrics to make a comparison.

Year  SAFE    UZR     PMR      Plus/Minus     SFR
     (Runs)  (Runs)  (Outs) (Balls fielded)  (Runs)
2003   -16    -21     -13         -14          -15
2004   -11      3     -30         -16            2
2005   -19    -11     -41         -34           -9
2006   n/a    -15     -18         -22           -8
2007   n/a     -7*    -40         -34          -20
* First half of the season only