Basic wOBA Equation

by
May 14, 2015

Here at FanGraphs and RotoGraphs, I occasionally delve into articles that look at split-data, and have had to create a simplified version of our wOBA formula in order to generate some numbers where wOBA isn’t easily available.

wOBA is simply a rate-stat version of a linear-weights calculation, but because the relative values of events change according to the run environment, the value of the different types of outcomes that go into the formula change from season-to-season. This is why why we publish the guts of wOBA, so that you can see exactly how to calculate wOBA for any given year.

But if you’re looking at multiple years including different run environments, it can be helpful to have a basic wOBA formula that gets very close to the results for any individual year, but includes static values and a set formula. To that end, I’ve created what I call Basic wOBA, which does exactly that; follows the year-by-year wOBA shifts very closely without needing to update the variables for each season. We’re not rolling this out as an official version of wOBA, and it won’t appear on the site itself, but it will be referenced occasionally in articles, and so it is helpful to have the formula listed as a reference for when it is called upon.

After some testing, here is the equation we decided to use:

Basic wOBA = (.7* (BB + HBP) + .9*1B + 1.25*2B + 1.6*3B + 2*HR)/PA

Looking back at players with more than 200 plate appearances since 1980, the R-squared between the actual wOBA and Basic wOBA is 0.986, with a value of 1.0 being a perfect 1:1 relationship. So while not perfect, it will give a nearly equal value in almost every case.

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If you see Basic wOBA referenced in an article, this is the formula that isbeing used.





 

Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR twice, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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suicide squeezeMember since 2016
10 years ago

I’m assuming that should be .725 for HBP? Otherwise, we’ve really been underrating Craig Biggio.

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