The Slash Stats

Last weekend, David Appelman posted the year-to-year correlations for UZR and wOBA by chances and plate appearances. The latter had a R^2 value of 0.30 for players with at least 500 plate appearances in both 2008 and 2009. Without a baseline as to how other offensive statistics fare, this seems like a pretty weak correlation. I similarly took all 101 batters with 500+ plate appearances in both seasons and ran the correlations on their batting average, on-base percentage, and slugging percentage to figure out where wOBA’s R^2 ranks. Here are the results:

Batting average: 0.1975 (0.444 R)
On-base percentage: 0.3673 (0.606 R)
Slugging percentage: 0.3653 (0.604 R)

Interestingly, OBP and SLG were nearly identical while BA shows just how volatile it is on a year-to-year basis. wOBA ranks just behind the two slash stats that make up OPS, so why do we use wOBA if it’s presumably less predictive on an individual basis than either of those components? Because it correlates to runs scored better than OPS. I ran the team production numbers versus runs scored and found these relationships (both R):

OPS: .958
wOBA: .960

This is why we use wOBA. It might not have the year-to-year relationship that OBP and SLG do, but it correlates with team runs scored about as well or better than anything else around. Now these numbers are not adjusted for park or league and are in their raw forms.

(For fun I used the equation given to estimate each team’s run totals in 2009. The unluckiest teams: Mets, Yankees, Astros, Mariners, and Nationals; the luckiest: Athletics, Angels, Giants, Dodgers, and Twins. Deeper analysis may or may not reveal something about those teams.)