Petti: Slowly backing away from the Pythag expectation

From SABR member Bill Petti at FanGraphs on August 22, 2012:

For most of 2012, the Baltimore Orioles have been playing over their heads. Well, at least when it comes to their expected win-loss record.

Based on the run differential the team has generated, the O’s have amassed 10 more wins than we would expect based on their Pythagorean winning percentage. The team has outplayed its cumulative expected winning percentage throughout the year and — since April — picked up two additional wins at the end of each month. If they sustain this performance and finish August with at least 10 more wins then their Pythagorean winning percentage would predict, they would be just the third team to do so since 2001 (the 2004 Yankees and the 2007 Diamondbacks are the other two).

Some might point to this glaring discrepancy between Baltimore’s actual winning percentage and Pythagorean winning percentage as evidence that the Orioles cannot sustain their winning ways. Of course, this raises the question of whether we really gain anything from a predictive standpoint heading into September if we focus on a team’s expected winning percentage rather than their actual performance.

The answer based on a review of the past decade seems to be no.

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Originally published: September 4, 2012. Last Updated: September 4, 2012.