Thursday, April 17, 2014
wOBA Primer
Terrific job by studes to getting inside wOBA, and explaining it for mass consumption.
***
I'll add one thing about the presentation of wOBA compared to the presentation of Linear Weights (LWTS): I've never had to explain negative values. Even though wOBA is completely dependent on the LWTS model, the user is never left scratching his head with what to do with one guy who is -10 runs in 600 PA and another guy who is -7 runs in 300 PA.
And similarly, you could compare wOBA to various forms of RC (including wRC), and you don't have to be confused with one guy having 82 RC in 600 PA and another having 46 RC in 300 PA.
Why do we have this issue? It's what I call the single-dimensional presentation problem. What we REALLY want is to present the data in TWO dimensions. For example, IP and ERA (or RA9). Those are perfectly presented, one as a "rate" stat, and the other as a quantity stat. Do we REALLY want to throw those two pieces of information away, and instead present "runs relative to average" or "runs relative to replacement"? We have one guy with a 3.00 ERA and 108 IP and another with a 3.75 ERA and 216 IP, in a league of 4.00 ERA. In terms of "runs relative to average", the first guy will come in at +12 and the second guy at +6. In terms of "runs relative to replacement", the first guy is +24 and the second guy is +30.
So, which is the better presentation, relative to average or relative to replacement? Beats me. Everyone has their own question, and by collapsing the two dimensions (quality and quantity) into one dimension, you lose half of your audience.
BUT, what if instead I present TWO dimension, and I say that the pitcher's "support neutral" W-L record is 7-4 for one guy, and 12-11 for the other guy. This now opens up possibilities for both groups to have a discussion. One guy can suggest, "hey, the first guy won 3 more than he lost", while the other guy might say "ok, but the second guy got 5 more wins and 7 more losses, so the first guy will need a backup who has to be at least as good as that". And if this backup would be 4 and 8, then we can see that the 7-4 record, while impressive, doesn't have enough quality to make up for the hole that the lack of quantity opened up.
So, doubling back to wOBA. By putting it on a rate scale, we are now forced to ALSO consider PA. Linear Weights and Runs Created, by presenting the number as some sort of combination of quality and quantity leave us asking if that combination is sufficient to answer our questions. And half of the time, the answer is no. Hence, the best thing to do is leave things in two-dimensions as much as you can.
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