Friday, February 22, 2013

OPS+ versus wRC+

Over the last few years, fans have become increasingly familiar with Adjusted OPS (OPS+), a statistic, first introduced by Pete Palmer back in the 1980s.  This OPS+ metric is OPS adjusted for league average and home ballpark.  It is useful because it allows us to compare players who played in different ballparks and/or different eras.  It is calculated using the following items:

OBP = On-Base Percentage
SLG = Slugging Average
MLB OBP = MLB Average OBP (with pitchers removed)
MLB SLG = MLB Average SLG (with pitchers removed)
BFP = Ballpark Factor

The formula is

OPS+ =  (OBP/MLB OBP + SLG/MLB SLG - 1) x 100/BPF

Using Miguel Cabrera's 2012 season as an example yields

OPS+ = ((.393/.324 + .606/.413 - 1) x 100)/ 102 = 165

In general, an OPS+ of 100 is average, an OPS+ of above 100 is above average and an OPS+ of less than 100 is below average.  There is a popular misconception that OPS closely matches the ratio of a player's OPS to league OPS.  However, an OPS+ of 165 does not mean that Cabrera had an OPS 65% better than league average.  We know it's a really high OPS+ because it was the highest in the American League, but it has no concrete meaning.

Another limitation of OPS+ is that it counts OBP and SLG the same when OBP actually contributes about 80% more to run scoring than SLG.  Thus, players who get most of their production from OBP will be short changed by both OPS and OPS+ .  At any rate, the OPS+ figures can be found at Baseball-Reference.com for all players.

The OPS+ metric is OK for many purposes as long as you understand the shortcomings.  If you want a more reliable statistic, you can use Weighted Runs Created Plus (wRC+), a creation of Tom Tango.  Because it is based on Weighted On-Base Average (wOBA), wRC+ more accurately weights batting events (1B, 2B, 3B, HR, BB, HBP, outs) than OPS does.

It is calculated as:

a = MLB Runs per PA ( with pitchers removed)
b = Park Adjusted wRAA/PA (with pitchers removed)
c = b/a + 1
wRC+ =c x 100

Cabrera had the following numbers in 2012:

a = .1164
b = 53.7/697 = .0770
c= .0770/.1164 + 1 = 1.66
wRC = 1.66 x 100 = 166.

Another benefit of wRC+ beyond it's accuracy is that it has a concrete interpretation.  In Cabrera's case, he created 66% more runs than would be expected by an average hitter in 697 PA.  The numbers for all players can be found at FanGraphs.com.

The wRC+ metric is on the same scale as OPS+ and does not generally produce wildly different results.  The biggest difference I found for the Tigers was Austin Jackson (135 wRC+ versus 130 OPS+).  The OPS+ vs. wRC+ comparison for the rest of the Tigers in 2012 is shown in Table 1 below.  The third colum is the percentile among players with 250 or more PAs.

The lesson to be learned here is that wRC+ is a little better than OPS+ and should be used for more serious evaluation of players.  However, if you prefer using the Baseball-Reference site, OPS+ is a reasonably good estimate of a player's relative hitting value in most cases.

Table 1: wRC+ versus OPS+ for Tigers, 2012


Player
OPS+
wRC+
PCTL
Cabrera
165
166
99
Fielder
152
153
97
Jackson
130
135
88
Dirks
130
133
87
Hunter (LAA)
132
130
85
Avila
100
104
52
Infante (DET/MIA)
93
92
34
Berry
86
89
29
Young
89
89
29
Peralta
85
86
24
Boesch
77
77
13
Santiago
52
55
1
Raburn
30
28
0


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