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Is WPA Predictive for Batters?

Posted By David Appelman On April 10, 2007 @ 2:59 pm In Research | 15 Comments

One of the biggest complaints I see about WPA is that it’s not predictive. The mere mention of it’s non-predictability seems to be enough for many to write it off as a mere toy used by some of stats community.

So let’s see how it actually correlates from year to year compared to the stats we all know, like AVG, OBP, SLG, and OPS. I’ll throw in Batting Runs Above Average for fun too.

Looking at the r-squared from 2005 to 2006 for batters with over 300 plate appearances, here’s how WPA stacks up against the regulars:

AVG: .12
WPA: .27
BRAA: .35
OBP: .36
OPS: .36
SLG: .38

Here’s the same deal, 2004 to 2005.

AVG: .14
WPA: .24
OBP: .27
OPS: .30
BRAA: .31
SLG: .33

It’s true, WPA doesn’t correlate as well from year to year as OBP, SLG, or OPS, but it does have some correlation from year to year. In 2004, a players OBP was almost indicative of his 2005 OBP as his 2004 WPA was of his 2005 WPA. Yet, that wasn’t quite the case in 2005 to 2006. BRAA which is calculated by using Run Expectancy on a play-by-play basis (much like WPA uses Win Expectancy), holds its own against the regulars.

Anyway, the point is, let’s stop using the argument that WPA isn’t predictive as a crutch, because it does actually show some correlation from year to year.

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