If you’re any sort of saberist, you should already know that Weighted On-Base Average (wOBA) is vastly superior to On-Base Plus Slugging (OPS) at measuring offensive value. While OPS is a mishmash statistic, throwing together OBP and SLG for kicks and giggles, wOBA was created based on research on the historical run values of events. It weighs all the different aspects of hitting in proportion to their actual, real-life value to a team’s offense.
But how exactly do these two statistics differ in assigning value to events? See for yourself:
What you see in that chart is a representation of how much wOBA and OPS weigh each individual outcome. The wOBA coefficients are very easy to find and straightforward, but I had to take some shortcuts to come up with coefficient values for OPS. While straightforward in theory – the sum of OBP and SLG – OPS is actually a rather convoluted statistic. You want to try adding these two stats together?
Instead of tangling with all that, I took the shortcut of just assuming both statistics had the same denominator and calculated the coefficients that way. It’s good enough for an estimate, and it gets the point across in the visual. So this is another area that wOBA trumps OPS: simplicity.
As you can see from the visual, wOBA puts more stress on walks, hit by pitches, and singles, while OPS attaches a huge value to homeruns and triples.* Since OPS is calculated by adding OBP and SLG, many people believe it treats both power and on-base skills as equally important, but that’s simply not true. When you dig down into the actual values OPS attaches to each outcome, it still favors power hitters by a wide margin.
*OPS also ignores Reached On Errors (ROE), but these happen so infrequently it isn’t a huge concern.
Also, when you look at OPS like this, doesn’t it seem slightly ridiculous? How can we treat it as a serious statistic when its coefficients look like they were created by a third grader? I’ll stick with the one backed by research and history, thank you very much.
For more on wOBA, see its page in the FanGraphs Saber Library.