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August 20, 2008

Prospectus Hit and Run

Park Adjusted Defensive Efficiency

by Jay Jaffe

Last week, in my look at the Twins' rotation, I made reference to this year's Park-Adjusted Defensive Efficiency statistics, and noted that the Twins were dead last in the American League in that category. I've been meaning to devote a column to the topic for quite a while, so at long last, it's time to get PADE.

For those in need of a refresher course, PADE is Baseball Prospectus alum James Click's method for bringing park effects to bear upon Bill James' Defensive Efficiency (DE) rate, which tells us how often a team turns a batted ball into an out. PADE compares each club's Defensive Efficiency at home to that on the road, incorporating a three-year park factor specific to DE (as opposed to runs, home runs, or another component stat) and the unique composition of each team's schedule. The end product tells us the percentage of balls in play above or below the major league average that each team converts into outs. A one percent difference may not sound like much, but extrapolating from Click's calculations, it's worth about 13 runs—more than one win in the standings.

When I dusted off PADE last fall (Click has moved on to a major league front office, but our data team of Bil Burke and Jason Paré has the special blend of herbs and spices necessary to whip up a fresh batch of figures), I discovered that the two teams which had just met in the World Series, the Red Sox and Rockies, finished first and second atop the year's list. That's a pretty decent advertisement for the utility of the number, particularly given that both teams in question play in very non-traditional ballparks that have the potential to obscure the quality of defensive play. According to the 2007 figures, the Red Sox, who led the AL in raw DE as well, were 3.22 percent above average in converting balls in play into outs after accounting for park effects. The Rockies were fourth in the NL in raw DE, and 3.07 percent above average when accounting for park. Bringing up the rear were the Brewers (-3.44 percent), Marlins (-3.86 percent), and Devil Rays (-5.64 percent).

I mention those numbers by way of introducing the 2008 PADE figures:

Team    DE   MLB DE  PkFactor  PADE
CHN   .7085   .692   0.9957    2.60
BOS   .6994   .692   0.9794    2.13
ATL   .7011   .692   0.9921    1.73
OAK   .7113   .692   1.0313    1.21
ANA   .6995   .692   1.0010    1.03
PHI   .6985   .692   1.0009    0.90
TBA   .7111   .692   1.0382    0.84
FLO   .6917   .692   0.9860    0.67
ARI   .6943   .692   0.9950    0.59
NYN   .7039   .692   1.0285    0.29
CLE   .6880   .692   0.9862    0.12
TOR   .7026   .692   1.0302    0.02
DET   .6923   .692   1.0008    0.01
BAL   .6960   .692   1.0133   -0.08
HOU   .6917   .692   1.0049   -0.28
MIL   .6976   .692   1.0245   -0.40
SLN   .6965   .692   1.0232   -0.50
SFN   .6832   .692   0.9933   -0.94
KCA   .6852   .692   0.9996   -0.96
CHA   .6897   .692   1.0134   -1.00
LAN   .6916   .692   1.0199   -1.03
COL   .6796   .692   0.9889   -1.23
SDN   .6940   .692   1.0307   -1.23
WAS   .6901   .692   1.0207   -1.30
NYA   .6843   .692   1.0240   -2.28
SEA   .6805   .692   1.0180   -2.54
MIN   .6844   .692   1.0436   -3.20
PIT   .6769   .692   1.0255   -3.41
TEX   .6708   .692   1.0157   -3.82
CIN   .6712   .692   1.0272   -4.30

A few notes before we dig in. First of all, the raw DE figures are displayed to the fourth decimal place because the teams are clustered rather closely, with a standard deviation of about 10 points. The DEs above are the ones from our Team Audit Pages, using the formula that incorporates Reached On Error numbers into the equation: DE = [1 - (H + ROE - HR) / (PA - BB - SO - HBP - HR)]. Our sortable stats report uses a simpler formula that's effectively DE = 1 - BABIP. We have the data to go beyond that, so I'll stop referring to the latter version to avoid confusion.