Birnbaum: The OBP/SLG regression puzzle

From SABR member Phil Birnbaum at Sabermetric Research on May 29, 2013:

I ran regressions in the previous posts to predict winning percentage from on-base percentage and slugging.  In those regressions, I had adjusted all teams to the league SLG and OBP.  I had to.  If you don't adjust, the results vary a lot.

Here's the regression completely unadjusted.  (It's all teams from 1961 to 2009, except strike seasons.)  Here's the equation.  (I'll put the OBP/SLG coefficient ratio in brackets too.)

wpct = (2.19*OBP) + (0.07*SLG) - .2405  [ratio: 30]

That's an OBP/SLG ratio of over 30!  We were expecting 1.7.  It seems like slugging barely matters at all!

Compare that to the "regular" regression, which adjusts for league-season: 

wpct = (2.70*OBP) + (0.89*SLG) - .7843   [ratio: 3]

OK, that's a bit better.  The ratio is down to 3.

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This page was last updated May 29, 2013 at 2:25 pm MST.