Is EqA better than wOBA?
Aaron (YYZ): Doesn’t the AL ROY almost have to be Elvis Andrus? He’s the 8th most valuable SS (by WAR) in all of baseball (and the 9th best SS offensively by wOBA)
Christina Kahrl: Why use wOBA when EqA’s testably more accurate?
BP has tested the accuracy of EqA before; however it’s notable that wOBA was not included in the comparison. So I thought I would run a quick test to see if EqA really is more accurate. I used this as my formula for calculating Equivelent Runs and this to calculate runs as per wOBA.
FanGraphs figures wOBA as far back as 1974, and if we extend that far back, looking at RMSE, we discover that in fact EqA bests wOBA by a slight amount in our typical tests, looking at team runs per season:
|
EqR
|
wOBA_R
|
|
|
Correl.
|
0.97
|
0.97
|
|
RMSE
|
27.3
|
27.6
|
|
MAE
|
21.4
|
21.9
|
I would go ahead and call that essentially a dead heat, but it wouldn’t be unreasonable to declare victory for EqA.
But of course the question was about Elvis Andrus in 2009, and from 1980 onwards the advantage shifts to wOBA. Narrowing it down to 1993-2008, the modern offensive era:
|
EqR
|
wOBA_R
|
|
|
Correl.
|
0.97
|
0.97
|
|
RMSE
|
28.3
|
27.5
|
|
MAE
|
21.9
|
21.7
|
Looking at RMSE, wOBA is better by about a run per season. I’d consider that more significant overall, and far more relevant to Elvis Andrus.
The problem is, aggregate accuracy is absolutely not the litmus test of a run estimator. Teams represent a very narrow profile of hitter. The vast majority will have an OBA .300-.350, a SLG .390-.470, a BA .250-.280, 140-210 HR. Thus, if the contant for a HR were ‘off’ by 20%, it could be balanced out by an offsettingly (hehe… nice word) bad singles constant…. since there is uch little diversity in team btting, it would rarely show a meaningful error. All systems (wOBA, RC, LWTS, BaseRuns, XR, ETC) are going to do 99.5% as well as the next in terms… Read more »
Adam, wOBA is simply a system of linear weights. n fact, what it really is is a method of expressing LWTS as a rate. Talking about wOBA’s accuracy is something of a red herring – you could do wOBA with Estimated Runs Produced or with my House weights if you wanted to, and the accuracy would be driven by the underlying weights. But wOBA the framework has become associated with a particular set of linear weights values produced by Tom Tango and used by Fangraphs, so 99% of the time when someone talks about the accuracy of wOBA that’s what… Read more »
Right… I understand the calculation of wOBA, and what you were trying to get across. Allow me to rephrase; I think my broader point is that ‘tests’ in general only tell you so much about a run estimator in terms of accuracy, because they can only measure it in the macro. We can’t say “RC says Carlos Pena produced 46 runs, but he ‘really’ produced 43”…. there’s just no way to do that. So we are forced to look at teams. But that’s a very narrow constraint, so that standard is irrelevant if we were to apply it to many… Read more »